Letters that come back: every AI model's reply, tested

Write a short story from this idea, with a title on the first line. Keep every name and detail in it, and give it a real ending.

---
A retired postman named Walter finds that every letter he delivered in 1987 is being returned to his door, one a day.

How the AI story generator's test inputs are scored, with every model's results on all five.

1. GPT-6 Luna

   Passed: Stated all 3 facts with the section.

   The Last Delivery
   
   On Monday morning, a letter lay on Walter’s doorstep. Its stamp was faded, its address familiar: Mrs. Bell, 14 Ash Street. Walter had delivered it in 1987.
   
   On Tuesday, another appeared. Then another, one each day, all the letters he’d carried that year, returned to his door.
   
   Walter kept them in a shoebox. He recognized the slanted handwriting, the old stamps, the places he’d walked in rain and sun. On Friday, he opened one addressed to the late Mr. Hales. Inside was a postcard Walter had never noticed before: “I’m sorry. Come home.”
   
   The next morning, a letter arrived addressed to Walter himself.
   
   He knew the handwriting at once. It was his own, from thirty-seven years ago. Inside was a note he’d written to his younger brother, Peter, then crossed out and never sent.
   
   I shouldn’t have let you leave angry. I miss you. Please come by.
   
   Walter sat at the kitchen table, the box open beside him. He remembered Peter’s last visit, their argument over their father’s house, the pride that had kept Walter silent afterward. He’d told himself there would be time.
   
   There hadn’t been.
   
   That afternoon, Walter took the shoebox to the post office. The clerk helped him find Peter’s address. Walter wrote a new letter, carefully this time, and paid for the stamp himself.
   
   “I’m sorry I waited,” he wrote. “If you’re willing, I’d like to see you.”
   
   For the first time since Monday, no letter came back the next morning.
   
   A week later, Peter stood on Walter’s doorstep, holding the letter. Walter opened the door.
   
   “You took your time,” Peter said.
   
   “I know,” Walter replied, and stepped aside.

   343 tokens in, 407 out (36 of them reasoning) · 4.9 s · $0.0001 · 1 message on Pro · answered by openai/gpt-6-luna via OpenAI · September 28, 2026

2. GLM 5.3 Flash

   Passed: Stated all 3 facts with the section.

   The Returned Letters
   
   The first envelope appeared on a Tuesday, wedged between the screen door and its frame. Walter recognized the handwriting before he recognized the name: Mrs. Estelle Crane, Maple Street, 1987. He'd carried that letter forty years ago, back when his route was Route 9 and his knees still worked.
   
   "Return to sender," was stamped across it in faded red ink.
   
   He opened it because a retired postman can't help himself. Inside, in Estelle's careful script, was a single line: "If you're reading this, I hope the rain stopped."
   
   It hadn't rained in days. But the day he'd delivered that letter, the spring of '87, it had poured so hard his mailbag leaked.
   
   The next morning there was another. Then another. One a day, each from his old route, each stamped 1987, each with a line that felt like it had been written just that week. One from the Hendersons said, "The dog misses you." Walter's old dog Buster had been gone a decade. Another, from the boy on Elm Street he used to wave to, read, "You always said the mailbox was a promise."
   
   On the ninth day, Walter stopped waiting by the door and walked the route instead. Rain dripped off his collar as he climbed Maple Street steps. Estelle was ninety now, sharper than ever.
   
   "You finally came," she said, holding her own returned letter. "I wrote fifty of them that year, asking you to stop by sometime. Coward's post."
   
   "Mine came back too," Walter said. "All of them."
   
   "Then I suppose," Estelle said, pouring two cups of tea, "the post office finally did its job. Delivered you."
   
   He drank the tea. The rain kept falling, and he found he didn't mind it at all.

   353 tokens in, 385 out · 39.4 s · $0.0002 · 1 message on Pro · answered by z-ai/glm-5.3-flash via Parasail · September 28, 2026

3. Claude Haiku 5.5

   Passed: Stated all 3 facts with the section.

   Return to Sender
   
   Walter Pruitt had carried the Maple Hollow route for thirty-one years, and he still knew the sound a mail slot made when a letter dropped through it. So on the first morning of the strange returns, he heard it before he saw it: a soft flap, then paper sliding across the hall floor.
   
   He picked up the envelope. It was addressed to Mrs. Ida Benning at 14 Cedar Court, in his own careful block capitals, with a 1987 stamp that showed a bald eagle. The postmark read March 3, 1987. Inside was the electric bill he had delivered to her that week, sealed and unopened, as if it had never left his bag.
   
   "Well, that's not right," Walter said to the empty kitchen.
   
   The next morning there was another. Then another. Each one was a letter he had carried in 1987, each returned to his own front door, one per day, always before the mail came.
   
   On the fifth day he called his daughter, Carla, who worked at the regional post office in Dayton. "Dad, that's impossible," she said. "Those letters were delivered. Or they were supposed to be."
   
   "Were they?" Walter asked. "Because I remember Ida Benning. She waited for a letter from her brother in Oregon. He never wrote. I carried a lot of nothing to that house."
   
   Carla was quiet for a moment. "Dad, check the one that came today."
   
   The envelope on the mat was thinner than the others. Walter slit it open. Inside was a single folded page in shaky handwriting: *Walter, I got your card in 1987, the one with the crooked stamp. You were the only one who ever stopped to say hello. I never wrote back. I'm sorry. Ida.*
   
   Walter sat down on the stairs. He had forgotten the card. He had put it in with the Benning mail in a hurry, the same week his own wife had moved out of state with her sister. He had never thought about either one again.
   
   He reached for the phone. Carla answered on the second ring.
   
   "Carla," he said, "I need you to find me a stamp. The kind with the eagle. And I need Ida's address, the new one."
   
   "Dad, she's ninety-one."
   
   "Then she's waited long enough for an answer," Walter said. "I'm going to write back."
   
   The next morning, for the first time in years, Walter walked to the corner box and mailed a letter himself, and the flag went up with a satisfying clack.

   447 tokens in, 773 out · 6.0 s · $0.0004 · 1 message on Pro · answered by anthropic/claude-haiku-5.5 via Anthropic · October 7, 2026

4. Gemini 3.8 Flash

   Passed: Stated all 3 facts with the section.

   The Year in the Mailbox
   
   Walter found the first one on a rainy Tuesday: an envelope yellowed at the edges, postmarked October 14, 1987. It was an electric bill addressed to the late Mrs. Gable, stamped with red ink that read "RETURN TO CARRIER." 
   
   He thought it was a prank by the boys down at the depot. But on Wednesday, an RSVP to a wedding long dissolved slid through his mail slot. On Thursday came a postcard from Mallorca, its colors faded to pastel. Every morning at dawn, the metal flap clattered, delivering precisely one piece of mail Walter had carried in his leather pouch thirty-six years ago. 
   
   By winter, three hundred envelopes sat in stacks on his kitchen table. Walter read them all. They formed a slow-motion tapestry of Oak Creek: grocery debts, quiet love affairs, and teenage apologies. The weight of an entire town's forgotten year was settling into his living room, but he could not understand why it was coming to him. 
   
   On the three hundred and sixty-fifth morning, the flap rattled one last time. Walter hurried to the door and picked up a lilac envelope. His chest tightened. It was postmarked December 31, 1987, addressed in his own youthful hand to Martha, the woman he had loved from afar and never dared speak to before she moved west. 
   
   Walter had slipped it into her box at sunset on his final run of that year, wondering for decades if she had ever read his confession. 
   
   He flipped the envelope over. On the back, in faint pencil dated yesterday, were three words: "I waited, Walter." 
   
   Walter set the letter on the table, took his winter coat from the hook, and stepped out the door toward the train station.

   358 tokens in, 374 out · 4.3 s · $0.0008 · 1 message on Pro · answered by google/gemini-3.8-flash via Google AI Studio · September 28, 2026

5. DeepSeek V4.1 Flash

   Passed: Stated all 3 facts with the section.

   The Returns
   
   The first letter arrived on a Tuesday, flat on Walter's doormat with no postmark, no stamp, nothing but his own block capitals from 1987: 14 ELMWOOD TERRACE.
   
   He turned it over twice. He remembered 14 Elmwood Terrace. He remembered the dog behind the gate and the woman who never came out.
   
   The next morning, another. Then another. One a day, always on the mat before seven, and Walter, who had walked thirty-one years of streets and knew every loose curb between the depot and the river, began to feel his old route walking him back.
   
   "Bernard," he said over the fence on Thursday, "do you ever get letters that shouldn't come?"
   
   Bernard was pruning a rosebush. "The gas bill comes whether it should or not."
   
   "It's not bills."
   
   By the ninth day the pile on his kitchen table was nine deep, and Walter opened the ninth because he was sixty-nine and tired of not knowing. Inside was a birthday card he had carried for a week in his bag in the spring of 1987, then never delivered, because Mrs. Ashcombe had moved out in the night and left no forwarding address. Someone had written across the card in his own handwriting: You had one more street to walk.
   
   He sat down hard on the chair.
   
   On the tenth morning there was no letter on the mat. There was only the green canvas bag.
   
   Walter walked the route. Elmwood Terrace first, past the gate with no dog now, then the long brick row on Culver Street, where he slid the birthday card through the slot and stood a moment in the cold. On Harlow Road he knocked on Marisol Vance's door and gave her the letter from 1987 that he had written and kept, the one he had been too afraid to post to the woman next door.
   
   She read it on the step. Her hands were not steady.
   
   "Thirty-eight years," she said.
   
   "I know it."
   
   "Well," Marisol said, and held the door open wider, "you're late. Come in and have some tea."
   
   He hung the bag on the back of her chair. In the morning, the mat was empty, and Walter went out anyway.

   370 tokens in, 718 out (255 of them reasoning) · 3.6 s · $0.0010 · 1 message on Pro · answered by deepseek/deepseek-v4.1-flash via Together · October 8, 2026

6. GLM 5.3

   Passed: Stated all 3 facts with the section.

   The Letters of 1987
   
   On the first morning, Walter found a single envelope on his doormat, addressed in faded blue ink to a Mrs. Ethel Crane of Willowbrook Lane. He knew the name. He had walked Willowbrook Lane six days a week for thirty-one years. But Ethel Crane had died in 1994, and the envelope smelled of dust and old rain.
   
   He turned it over. Stamped across the back, in red: RETURN TO SENDER — DELIVERED WITH REGRET.
   
   The second day brought another. A birthday card for Tommy Ferrell, age eight, now a man of forty-four living somewhere in Australia. The third, a love letter to Dora Pilkington from a sailor whose name Walter had never known. Each morning, one letter. Each one a hand he had once placed through a letterbox.
   
   "Someone's playing a joke," said his neighbor Maureen over the garden fence. "Report it."
   
   But Walter didn't. He began keeping the letters in a shoebox, and at night he read the postmarks like tea leaves. On the eleventh day came a letter addressed to himself, 1987, in his own careful postman's hand. Inside was a note in pencil: You missed one. Number 14 Bellamy Court. You were tired that day. It was raining.
   
   Walter sat very still. He remembered. A gray envelope, tucked in his satchel's torn lining, never delivered, and he had been too ashamed to confess it. The letter had been from a son to his dying father, and the father had gone without it.
   
   The twelfth morning, the shoebox was empty except for one final envelope. Walter carried it himself to Number 14 Bellamy Court, now a young couple's home, and left it on the step with a note: For the family of Harold Bemis, wherever they are.
   
   That afternoon, the postman brought Walter ordinary mail for the first time in weeks. He opened his own door, and it creaked like a gate finally swinging shut.

   353 tokens in, 428 out · 3.6 s · $0.0021 · 1 message on Pro · answered by z-ai/glm-5.3 via Friendli · September 28, 2026

7. GPT-6.1 Sol

   Passed: Stated all 3 facts with the section.

   Return to Sender
   
   The first letter arrived on Monday, without a stamp or a postmark.
   
   Walter recognized the envelope. In 1987, he had delivered it to Mrs. Bell, who’d cried before she even opened it.
   
   Now, thirty-nine years later, someone had pushed it through his door.
   
   On Tuesday came a birthday card. Wednesday brought a gas bill. Each morning, one more letter from his old route appeared on the retired postman’s mat.
   
   He kept them in delivery order. After a month, he needed the dining table.
   
   Then came the blue envelope.
   
   Walter sat down.
   
   He had carried it in his bag for three days in November 1987, afraid to deliver it to his own house. His daughter Ruth had written after their quarrel. Finally, he had left it on the kitchen table, unopened.
   
   His wife had put it away. Walter had never asked where.
   
   This time, he opened it.
   
   Dad,
   I’ll be at the station on Saturday. If you come, I’ll know we can try again.
   
   He reached for the telephone, then stopped. They spoke at Christmas. He knew her number, but not whether she still wanted him to call.
   
   At last he dialed.
   
   “Ruth? I found your letter.”
   
   There was a long silence.
   
   “I waited until the last train,” she said.
   
   “I know. I’m sorry.”
   
   Another silence.
   
   Then: “You could come Sunday.”
   
   He took the early train.
   
   When Walter returned that evening, a letter waited on his mat: a grocery order for a shop demolished years ago. The returns had not stopped.
   
   He placed it beside the others, then cleared a space on the table for the photograph Ruth had given him.
   
   Next Sunday, she was coming to lunch.

   343 tokens in, 360 out · 7.8 s · $0.0021 · 1 message on Pro · answered by openai/gpt-6.1-sol via OpenAI · September 29, 2026

8. Claude Haiku 4.5

   Passed: Stated all 3 facts with the section.

   Walter's Return
   
   The first envelope arrived on a Tuesday morning, slipped under Walter's door by no one he saw. It bore a postmark from April 1987—thirty-seven years ago. Walter recognized his own handwriting on the address: Mrs. Chen, Maple Street. He'd delivered that letter himself, as a postman for the city. Inside was a recipe for dumplings, never claimed by its sender.
   
   The next day, another came. Then another. One per day, always from 1987, always addressed in his careful script. Walter began to keep them in a shoebox, bewildered. He'd retired five years ago. Why now?
   
   By the third week, he understood. Each letter bore a return-to-sender stamp in red ink, but no postmark showing when they'd been returned. The addresses were all from his route that year: a love letter to someone named James; a college acceptance to a girl named Sophie; a custody notice to a man named Robert. None had reached their destinations.
   
   Walter sat at his kitchen table with the latest envelope and picked up his phone. He called the postal service's archives, then local directories, then old acquaintances. He began to track them down.
   
   Sophie never went to college. James moved overseas heartbroken. Robert lost custody of his daughter.
   
   Walter spent two months finding them. He mailed each person their original letter with a note: "This was meant for you in 1987. I'm sorry it never arrived." He included his phone number.
   
   The calls came slowly. Tears. Questions. Some forgiveness. Sophie wept and said she'd always wondered. Walter had no explanation for how the letters had returned, only that they finally had. On the day the last letter was delivered, nothing came under his door. The box was empty. Walter sat alone, the weight of thirty-seven years finally lifted.

   360 tokens in, 404 out · 6.5 s · $0.0024 · 1 message on Pro · answered by anthropic/claude-haiku-4.5 via Azure · September 28, 2026

9. Gemini 4 Argon

   Passed: Stated all 3 facts with the section.

   Return to Sender
   
   The brass slot rattled at dawn. Walter knelt in the hallway, his knees popping, and picked up a cream envelope stamped October 14, 1987. It was the two-hundredth letter to arrive since March, one each morning, every single one from his old Elm Street route thirty-seven years ago.
   
   He carried it to the kitchen table and stacked it beside yesterday's electric bill for the Hendersons and Tuesday's postcard from Florida. None bore a "Return to Sender" mark. They were sealed, crisp, and smelled of rainwater and the leather of his old mailbag. 
   
   "Still coming, Walt?" asked Clara from across the hedge when he stepped onto the porch with his coffee. In 1987, she had been the dark-haired girl at number forty-two. Now her hair was silver, like his.
   
   "October fourteenth today," Walter said, holding up the cream envelope. He squinted at the faded blue ink. "Wait. This one is addressed to you."
   
   Clara set down her pruning shears and walked over to the porch steps. Her hand trembled as she took it. The return address in the corner belonged to a young man named Thomas, who had moved to Chicago that autumn. 
   
   "I waited all October for him to write," Clara whispered, tearing the flap open. "When he didn't, I thought he'd forgotten me."
   
   Walter gripped the porch railing. He remembered October fourteenth: a torrential downpour, a overflowing storm drain by the corner mailbox, and a soggy handful of letters slipping from his wet fingers into the dark rushing water. He had been too afraid of losing his pension to report it.
   
   "Clara, I dropped a bundle in the flood that day," Walter said, his voice cracking. "I never told a soul."
   
   Clara read the page, a tear tracking through the garden dust on her cheek, and then looked up at him with a crooked, forgiving smile. "Well, you're late, Walter. Come inside and help me write him back, and let's see who else is in your kitchen."
   
   Together they went through the front door, ready to deliver thirty-seven years of overdue news.

   390 tokens in, 466 out · 10.5 s · $0.0027 · 1 message on Pro · answered by google/gemini-4-argon via Google AI Studio · October 15, 2026

10. Kimi K3

    Passed: Stated all 3 facts with the section.

    The Letters of 1987
    
    Walter Pribble had been retired six years when the first letter arrived. It lay on his doormat in a yellowed envelope, stamped RETURN TO SENDER, addressed in handwriting he recognized as belonging to Mrs. Abernathy of Chestnut Lane, who had been dead for a decade.
    
    The postmark read June 3, 1987.
    
    "Some prank," Walter muttered, setting it on the kitchen table. But the next morning brought another, and the morning after that. One a day, always letters he remembered delivering, back on his old route, in the last full year before his knees went bad.
    
    He opened the seventh one. It was from a young soldier to his sweetheart, full of plans for when he came home. Walter remembered delivering it. He also remembered the sweetheart had moved away a week before it arrived, and he had forwarded it without a second thought.
    
    Except here it was, unforwarded. Unopened.
    
    Walter sat down heavily. "What do you want from me?" he asked the growing stack.
    
    On the fortieth day, he opened one addressed to himself, in his own young handwriting. He had written it to his brother Tom during their long silence, and never sent it. He'd carried it in his satchel for a month, then tucked it away.
    
    The letter said only: I'm sorry. Come home for Christmas.
    
    Walter picked up the phone and dialed a number he still knew by heart. When a voice answered, older and rougher, Walter said, "Tom. It's Walt. I found something I should have delivered thirty-eight years ago."
    
    The letters stopped the next morning. But Walter kept writing his own.

    430 tokens in, 399 out (37 of them reasoning) · 11.6 s · $0.0040 · 1 message on Pro · answered by moonshotai/kimi-k3 via Wafer · September 28, 2026

11. GPT-6 Sol

    Passed: Stated all 3 facts with the section.

    The Return Route
    
    The first letter arrived on Walter’s doorstep on a Monday. It was addressed to Mrs. Bell, who had lived above the bakery until it closed. The postmark read 1987.
    
    Walter, a retired postman, knew the envelope. He remembered climbing those stairs with it in his bag.
    
    The next day brought a letter for the school caretaker. The day after that, one for the baker. Every morning, another letter Walter had delivered in 1987 waited at his door.
    
    He found Mrs. Bell at a care home and put her letter in her hand. She studied the handwriting, then laughed and cried at once. “My sister,” she said. “She always wrote the address too small.”
    
    Walter began carrying each day’s letter to its old recipient, or to someone who could tell him where that person had gone. Some doors opened. At others, he came away with an address or a story.
    
    On the twenty-third morning, the letter was addressed to Walter. His daughter June had written it when she was twelve. He remembered reading it at the kitchen table, but opened it again.
    
    Can I come on your route tomorrow? I’ll be quiet. I want to see where you go.
    
    He had told her no. There had always been another day to take her, until there wasn’t.
    
    Walter called June. “I found your letter,” he said.
    
    “I remember.”
    
    “I’m sorry I didn’t take you.”
    
    For a moment, he heard only her breathing. Then she said, “Where are you going today?”
    
    The next morning, a new letter lay on the step. June was waiting beside it, holding two pairs of walking shoes.

    343 tokens in, 1,210 out (864 of them reasoning) · 13.9 s · $0.0064 · 1 message on Pro · answered by openai/gpt-6-sol via OpenAI · September 28, 2026

12. DeepSeek V4 Pro

    Passed: Stated all 3 facts with the section.

    The Year That Came Back
    
    Walter had been retired eleven years when the first letter landed on his mat, postmarked March 2, 1987. It was addressed to a Mrs. Elsie Hart on Poplar Lane, but the house number was his own. No return address. He set it by the kettle and forgot it until the next morning, when another arrived. April 14, 1987. Then May 1. One a day, without fail.
    
    He spread them across the dining table. He knew every street, every name. He had carried those envelopes through rain and snow. Now they came back to him as if he were the last mailbox left. He didn't open them.
    
    His neighbor called over the fence, "Walter, you've got enough mail to start a library." Walter said, "They're mine now."
    
    After six months, a letter arrived addressed to Walter himself. It was postmarked December 31, 1987. He tore it open. Inside was a single sheet: "You delivered 41,208 letters that year. This is the last one. Thank you."
    
    He looked out at the street. The mailbox flag was down. No more letters came. Walter folded the sheet, put it in his pocket, and walked to the post office to hand in his carrier badge, though he had already retired. He felt lighter, as if he had finally delivered something to himself.

    344 tokens in, 1,659 out (1,369 of them reasoning) · 16.7 s · $0.0068 · 1 message on Pro · answered by deepseek/deepseek-v4-pro-0813 via Wafer · October 8, 2026

13. Claude Sonnet 5

    Passed: Stated all 3 facts with the section.

    The Last Round
    
    Walter Hobbes had carried the same leather satchel for thirty-one years, and when he retired he thought he was done with letters for good. So it surprised him, that October morning, to find an envelope on his doorstep addressed to a house that no longer existed on Marigold Lane, postmarked 1987, stamped RETURN TO SENDER in faded red ink, with his own name and address written beneath it in a shaky hand he didn't recognize.
    
    He opened it anyway. Inside was a birthday card, unsigned, meant for a girl named Ruthie Coyne. Walter remembered her house — pink shutters, a dog named Baxter. He remembered delivering that very card, thirty-six years ago.
    
    The next morning there was another. A letter to a soldier overseas, the paper gone soft and yellow. The morning after that, a wedding invitation to an address that was now a parking lot.
    
    Walter began keeping them in a shoebox, one a day, like a strange tide bringing back everything the years had swallowed. He started walking the old route again, knocking on doors, asking if anyone remembered Ruthie Coyne or the soldier, Private Daniel Marsh, or the couple who never got married. Most doors shut politely. A few didn't.
    
    He found Ruthie two towns over, gray-haired now, running a flower shop. She cried when she saw the card. "I always wondered why no one wished me happy birthday that year," she said. He found Daniel Marsh's sister, who wept for a different reason — her brother had died two months after that letter was mailed, in a place called Panjshir, and it had never reached him in time.
    
    On the thirty-first day, no letter came. Walter sat on his porch with the empty shoebox, and understood, at last, that every letter had found its way home — even the ones with nowhere else to go. He closed the box and, for the first time since retiring, felt his route was finally finished.

    445 tokens in, 625 out (9 of them reasoning) · 9.5 s · $0.0071 · 1 message on Pro · answered by anthropic/claude-sonnet-5 via Anthropic · September 28, 2026

14. Claude Sonnet 5.5

    Passed: Stated all 3 facts with the section.

    The Return of 1987
    
    On Monday morning, a yellowed envelope lay on Walter's doormat. He turned it over. The stamp was a first-class Queen in faded pink, and the address read *Mrs. E. Hartley, 14 Corn Lane.* Beneath it, in his own cramped hand, was a pencil tick.
    
    He had been retired eleven years. He still knew that tick.
    
    Tuesday brought another, for a Mr. Pruitt on Mill Road. Wednesday, a fat parcel-sized envelope for the Dunmore twins. By Friday Walter had a neat row on the mantel and a habit of standing at the window at seven, waiting for the thump.
    
    "Someone's playing a trick," said his neighbour Dot, over the fence.
    
    "Nobody's been near the door," Walter said. "And they're all sealed. Every one."
    
    He could not bring himself to open them. Instead he began remembering. Corn Lane had a dog that hated his bicycle. Mill Road smelled of bread from the bakery. In 1987 he had been forty-one, with a wife named Joan who packed him sandwiches and a satchel that bit into his shoulder.
    
    On the twelfth day the letter was addressed to *Joan Marsh, 3 Alder Close.* It was his own address then, and her maiden name. There was no return address. Walter sat down heavily.
    
    He had no memory of delivering it. Yet the tick was there, and beside it, a second mark he had never made: a small, careful *X*.
    
    He opened it at last. Inside was a single page in Joan's handwriting, dated March 1987. *Walter, if you read this, I have lost my nerve and asked the post to be braver than I am. I wanted to say that the satchel is too heavy and so are your silences. Talk to me. I will listen.*
    
    She had died in 2009. He had never known she wrote it. Somehow it had been sorted, ticked, and lost in the pile for thirty-seven years.
    
    The next morning the mat was empty. So was the one after. The row on the mantel was complete but for the last letter, which he understood now had been the only one that mattered.
    
    Walter took down the good notepaper. He wrote, slowly, *Joan, I am listening.* Then he walked to the pillar box on the corner, the first time in years he had posted anything, and let it fall.
    
    It made a soft, final sound, and for once he did not wait for the reply.

    447 tokens in, 782 out · 9.5 s · $0.0087 · 1 message on Pro · answered by anthropic/claude-sonnet-5.5 via Anthropic · September 28, 2026

15. Mistral Large 4

    Passed: Stated all 3 facts with the section.

    The Return Route
    
    Retired postman Walter sorted the mail when a yellow envelope slid out. The stamp showed a 1987 penny, and across the front, someone had written Return to Sender. He turned it over. No return address.
    
    The next morning, another appeared, addressed to 44 Birch Street. Walter recognized the street. He had delivered that letter thirty-seven years ago, slipping it into a green mailbox. That afternoon, he drove to 44 Birch and found only a vacant lot where a Victorian house had burned in 1987.
    
    Each day brought another envelope. A love letter to a soldier. A recipe card. A child’s crayon drawing. Walter pinned them to his refrigerator, a constellation of his old route. On the fourteenth day, the final letter arrived. Inside was a photograph of a woman named Clara holding a baby, with a note: For the family at 12 Elm Avenue.
    
    Walter knew that address. He had delivered that envelope on a Tuesday in 1987, watching the mother take it from the mailbox. Now the house stood empty, its windows dark. He knocked. No answer.
    
    He found Clara in the phone book. She lived three miles away, above a bakery.
    
    Walter stood on her doorstep holding the stack of envelopes.
    
    “I was the postman,” he said. “These came back to me. I think they were never truly delivered.”
    
    Clara took the photograph, her hands trembling. “My mother wrote every week. The letters stopped after the fire.”
    
    Walter had not known. He had simply moved to the next house.
    
    That evening, he wrote a letter of his own. He stamped it with a 2024 penny and placed it in his mailbox, addressed to Clara, telling her that some mail, like some love, takes thirty-seven years to arrive. The next morning, it was gone, delivered forward, finally reaching the person who had been waiting.

    346 tokens in, 4,390 out (4,367 of them reasoning) · 111.4 s · $0.0094 · 1 message on Pro · answered by mistralai/mistral-large-4-0 via Mistral · October 9, 2026

16. Grok 4.7

    Passed: Stated all 3 facts with the section.

    The Route That Came Home
    
    Walter found the first letter before the kettle boiled. It lay faceup on his mat, soft at the corners, addressed to Mrs. Alma Keene on Birch Lane. He had carried that street every morning in 1987. The stamp was his old red one, the one he used when the office ink ran out.
    
    He set it on the kitchen table and did not open it.
    
    The next morning there was another. Then another. One a day, always before dawn. A birthday card. A thin blue airmail. A bill with a coffee ring. Walter stacked them by street until the wood vanished. He walked the rooms at night, counting, as if the route might still be finished by morning.
    
    On the nineteenth day his neighbor Ellis knocked, a wet envelope in his hand.
    
    "This blew into my hedge," Ellis said. "It's got your stamp on the back."
    
    Walter turned it over. His name was on the front. Inside, in a younger hand, he had written to Alma's son and never posted it. I kept your mother's letter through the storm. I am sorry. I will bring it tomorrow.
    
    He had not brought it. The storm took the bag. Pride took the rest.
    
    That afternoon Walter walked Birch Lane with both envelopes. Alma's house was a bakery now. He left them with the woman at the counter.
    
    "For whoever still wants them," he said.
    
    She nodded and slid them under the till, where the warm bread would keep them flat.
    
    The next morning the mat was empty. Walter made his tea, put on his coat, and stepped out before the kettle sang. For the first time in years, the day began with him.

    1,576 tokens in, 1,361 out (1,014 of them reasoning) · 23.3 s · $0.0096 · 1 message on Pro · answered by x-ai/grok-4.7 via xAI · October 2, 2026

17. Gemini 3.1 Pro

    Passed: Stated all 3 facts with the section.

    Return to Sender
    
    Walter stooped to pick up the yellowed envelope from his welcome mat. He rubbed his thumb over the faded ink. The postmark read October 4, 1987. The retired postman recognized the looping handwriting instantly. He had delivered this exact envelope to the Miller farm thirty-five years ago.
    
    The next morning, another letter waited by his boots. The day after that, a postcard from a long-closed diner sat on his porch. One a day, every piece of mail he had routed in the winter of 1987 was appearing at his door, unopened and bearing the same vintage stamps.
    
    Walter stacked them on his kitchen table. He tapped the newest arrival against his coffee mug. "I did my job," he muttered to the silent room. "Why are you coming back to me?"
    
    He held up a pink envelope addressed to a Sarah Jenkins. He remembered Sarah. She used to wait by the front gate for the mail. She would be in her fifties now. Walter looked at his quiet, empty house, and then at the growing pile of undelivered history.
    
    He climbed into his attic and pulled his old canvas mail satchel from a dusty trunk. He packed the returned letters inside, slung the thick strap over his shoulder, and walked out the door.
    
    Walter marched down Elm Street and knocked on a familiar green door. A middle-aged woman answered, looking confused at the old man on her porch.
    
    "Special delivery for Sarah," Walter said, handing her the pink envelope. "It is thirty-five years late, but the post office never forgets."
    
    Sarah stared at the childhood letter, a bright smile breaking across her face. Walter adjusted his satchel, feeling the comforting, familiar weight on his shoulder. He had a route again.

    358 tokens in, 1,621 out (1,248 of them reasoning) · 14.7 s · $0.0101 · 1 message on Pro · answered by google/gemini-3.1-pro-preview via Google AI Studio · September 28, 2026

18. GPT-6 Astra

    Passed: Stated all 3 facts with the section.

    Return Address
    
    The first letter arrived on Monday, forty years late.
    
    Walter, a retired postman, recognized the blue envelope. In 1987, he had delivered it to Mrs. Bell, who had tipped him with tomatoes.
    
    Now it lay on his doorstep, marked UNDELIVERED.
    
    One arrived every morning. A birthday card. A gas bill. An airmail envelope thin as onion skin. Walter checked his old route notebooks: every letter was one he had delivered in 1987.
    
    On Thursday, he took Mrs. Bell’s envelope to her son.
    
    “She died last spring,” Martin said.
    
    “Perhaps this belongs to you.”
    
    Martin read it in the doorway. Then he sat down.
    
    “My brother asked her to come to his wedding. She always said he hadn’t.”
    
    “Didn’t I deliver it?”
    
    “You did.” Martin rubbed his eyes. “That wasn’t the problem.”
    
    The next morning brought a letter Walter knew before he picked it up.
    
    His own handwriting. His daughter’s old address.
    
    He had slipped it through her letterbox during his round after their argument. He remembered being proud that he hadn’t knocked.
    
    The envelope was still sealed.
    
    Walter carried it across town to the house where she lived now.
    
    Clara opened the door with a paintbrush in her hand.
    
    “Your letter’s come back,” he said.
    
    “I wondered when you would.”
    
    He started to offer it, then put it in his pocket.
    
    “I shouldn’t have told you to leave.”
    
    Clara set down the brush.
    
    “No,” she said. “You shouldn’t.”
    
    They stood there until she stepped aside.
    
    The letters kept arriving, one a day. Walter bought a shoulder bag and began his old route again.
    
    On Sundays, he left it by Clara’s door and stayed for dinner.

    343 tokens in, 367 out · 40.9 s · $0.0109 · 1 message on Pro · answered by openai/gpt-6-astra via OpenAI · September 28, 2026

19. Claude Opus 5.5

    Passed: Stated all 3 facts with the section.

    The Last Round of 1987
    
    The first letter arrived on a Tuesday, slipped under Walter's door with a faded 1987 postmark and his own initials pencilled in the corner, the way he'd always marked a delivery.
    
    "Mrs. Harlow, 14 Elm Street," he read aloud to the empty kitchen. "I brought you this myself."
    
    The next morning came another. Then another. Birthday cards, electricity bills, a postcard from Spain. Every one was a letter Walter had carried, and every one had come back to him, one a day.
    
    By March, his neighbour Priya found him on the step with a shoebox full of them.
    
    "Walter, you look like you've seen a ghost."
    
    "Just a year," he said. "The whole of 1987, coming home."
    
    He started walking his old route again, knocking on doors. Most of the names had moved or passed on. But at number 9, a man laughed at a report card from his childhood, and at the corner house, a woman cried over her late father's handwriting and hugged Walter on the doorstep.
    
    Then, on a grey Sunday, a letter arrived that he had never delivered.
    
    The envelope was stiff and unmarked by his pencil. He remembered it at once: the morning it slid behind the sorting cabinet, and the day he found it too late, too ashamed to say.
    
    "Miss Eleanor Voss, 22 Birch Lane."
    
    Birch Lane had become a care home. Eleanor was ninety, sitting by the window. Her hands shook as she opened it.
    
    "He did write," she whispered. "He asked me to wait."
    
    Walter held her hand while she read it twice.
    
    The next morning, nothing came under his door. Walter made tea, sat by the window, and found he didn't need anything to.

    447 tokens in, 853 out (292 of them reasoning) · 12.2 s · $0.0188 · 1 message on Pro · answered by anthropic/claude-opus-5.5 via Google · September 28, 2026

20. Claude Fable 5.1

    Passed: Stated all 3 facts with the section.

    The Return Route
    
    The first one came on a Tuesday. Walter found it on his mat: a pale blue envelope, postmarked March 1987, addressed to a Mrs. Ida Cullen at 14 Larch Street.
    
    "I put this through her door myself," he told the cat. "I remember the brass flap. It bit."
    
    He walked it round to Larch Street. Number 14 had new windows and a young man who had never heard of Ida Cullen.
    
    The next day, a gas bill for the Pattersons. Then a birthday card, still sealed, for a boy named Dean. Then a letter with a hospital crest that Walter remembered carrying carefully, the way you carry a full cup.
    
    By the second week his kitchen table was covered. He laid them out in order of the old route: Mill Lane, Larch Street, the flats behind the chapel. Every address he had walked in 1987. Every one coming back, one a day, as if the town were quietly handing his year back to him.
    
    "Someone's having a joke," his daughter Ruth said on the phone.
    
    "Nobody jokes with this much postage."
    
    On the twentieth day the envelope was cream-coloured and addressed in his own handwriting. To Margaret, at their old flat. He had never posted it. He had put it in his bag that morning in November, meant to leave it on the table for her, and by evening she had already gone.
    
    He sat with it a long time before opening it. It said only: Stay. I'll do better.
    
    Walter got his coat. He did not know where Margaret lived now, but Ruth did, and Ruth had been waiting years for him to ask.
    
    The next morning, for the first time in three weeks, the mat was empty.

    447 tokens in, 534 out · 12.0 s · $0.0312 · 1 message on Pro · answered by anthropic/claude-fable-5.1 via Google · September 28, 2026

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