pruneMessages leaves reasoning files when reasoning is set to all

[brennanbutler01]

Description

pruneMessages({ reasoning: 'all' }) removes reasoning text parts but leaves reasoning-file parts. reasoning: 'before-last-message' also leaves reasoning files in older messages.

This means intermediate reasoning images remain in history and are sent to the next model call even when the caller explicitly removes reasoning. I reproduced that with responseMessages from both generateText and streamText using the SDK test model.

Expected: remove both kinds of reasoning in the selected messages, while keeping regular file and text parts. Preserve reasoning in the last message for before-last-message.

The filter on current main only checks part.type !== 'reasoning'.

Related: #13430 concerns reasoning left behind after pruning tool calls; #11036 concerns OpenAI references after pruning. This report is about explicitly pruning the reasoning-file content type, without tool calls or provider metadata.

Reproduction

No API key or provider request is needed. In an empty directory:

npm init -y
npm install --ignore-scripts --save-exact ai@7.0.106 zod@4.4.3
node repro.mts

Save as repro.mts and run with Node 22.20+ or 24:

import { pruneMessages, type ModelMessage } from 'ai';

// Synthetic one-pixel PNG, representing an intermediate reasoning image.
const image = 'iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAIAAACQd1PeAAAADElEQVR4nGP4//8/AAX+Av4N70a4AAAAAElFTkSuQmCC';
const messages: ModelMessage[] = [{
  role: 'assistant',
  content: [
    { type: 'reasoning', text: 'Intermediate reasoning.' },
    { type: 'reasoning-file', mediaType: 'image/png', data: image },
    { type: 'file', mediaType: 'image/png', data: image },
    { type: 'text', text: 'Done.' },
  ],
}];

const pruned = pruneMessages({ messages, reasoning: 'all' });
console.log(pruned.flatMap(message =>
  typeof message.content === 'string' ? [] : message.content.map(part => part.type),
));
// Actual:   ['reasoning-file', 'file', 'text']
// Expected: ['file', 'text']

The fix appears to be extending the existing filter:

content: message.content.filter(
  part => part.type !== 'reasoning' && part.type !== 'reasoning-file',
),

Local tests cover both pruning modes, empty-message handling, ordinary file preservation, unchanged input history, and a second model call using pruned SDK-generated history. There are 6 failing regressions and 6 passing controls on both tested package versions and Node runtimes. Testing the current-main helper in isolation gives the same result; the proposed filter change makes all 12 pass. Full upstream suites have not been run. The reproduction passes strict TypeScript checking.

I used AI assistance to investigate and prepare the synthetic reproduction, tests, and proposed change.

AI SDK Version

• ai: 7.0.101 and 7.0.106 (unmodified npm packages)
• zod: 4.4.3
• Node.js: 22.20.0 and 24.13.0
• Main helper tested in isolation at 9528712c364c6cb46caf97b901bb742d0c623cd7; the full main checkout was not rebuilt.

Code of Conduct

• I agree to follow this project's Code of Conduct

[ai-sdk-factory]

Identify issue type

Identified as Bug
Confidence: High

Rationale

This is a concrete failure of existing reasoning-pruning behavior: one reasoning content type is removed while another is unexpectedly retained despite explicit pruning.

Evidence

• pruneMessages({ reasoning: 'all' }) removes reasoning parts but incorrectly retains reasoning-file parts.
• The same failure occurs for older messages with reasoning: 'before-last-message', causing reasoning images to remain in subsequent model history.
• A minimal reproduction shows actual output ['reasoning-file', 'file', 'text'] instead of expected ['file', 'text'] on released SDK versions and current main logic.

[ai-sdk-factory]

Bug Reproduction - AI SDK 7

Bug was reproduced.

Branch: main
PR: successful reproduction pull request

Details

• examples/ai-functions/src/reproduction/prune-messages-reasoning-files.ts reproduces the bug on main at 9528712c36.
• reasoning: 'all' removes reasoning text but retains reasoning-file; regular file and text parts remain intact.
• reasoning: 'before-last-message' retains reasoning-file in older messages while correctly preserving all reasoning in the last message.
• The failure occurs with synthetic messages and responseMessages produced by both generateText and streamText; the retained reasoning file is forwarded to a subsequent model call.
• A message containing only reasoning text and a reasoning file incorrectly remains after pruning instead of being removed as empty.
• packages/ai/src/generate-text/prune-messages.ts filters only part.type !== 'reasoning', omitting the supported reasoning-file content type.

[ai-sdk-factory]

Bugfix - AI SDK 7

Created bugfix and opened PR: #21121

Root Cause

pruneMessages filtered only reasoning parts even though assistant content also supports reasoning-file; the immutable reproduction confirmed those files remained in both generated and streamed histories.

Summary

Updated reasoning pruning to remove both reasoning and reasoning-file parts, added regression coverage, removed reproduction-only artifacts, and added a patch changeset.

Testing

Added tests covering both reasoning-pruning modes, regular file and text preservation, input immutability, last-message preservation, and removal of messages emptied by pruning.