feat: Thought signature support by Takshil-Kunadia · Pull Request #20 · WordPress/ai-provider-for-anthropic

Takshil-Kunadia · 2026-04-28T11:26:38Z

Closes #14

Summary

Round-trips MessagePart::thoughtSignature on the Anthropic adapter so multi-turn extended-thinking + tool-use exchanges work. Without it, Anthropic API rejects the request because the signature field is missing.

Test plan

Inbound verified the Title_Generation Ability in Abilities Explorer, with vendor temporarily upgraded to php-ai-client 1.3.1 and extended thinking. Captured a 384-char signature on the inbound MessagePart.
Outbound verified with a multi-turn CLI test: turn 1 produced a thinking + tool_use response; turn 2 echoed the assistant message back (with the captured signature) together with a tool_result. Anthropic accepted turn 2 and returned the final answer confirming the signature field is correctly serialised in the outbound JSON.

github-actions · 2026-04-28T11:32:13Z

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: Takshil-Kunadia <takshil@git.wordpress.org>
Co-authored-by: jeffpaul <jeffpaul@git.wordpress.org>
Co-authored-by: JasonTheAdams <jason_the_adams@git.wordpress.org>
Co-authored-by: felixarntz <flixos90@git.wordpress.org>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

Takshil-Kunadia · 2026-04-28T11:33:39Z

@felixarntz separate question while you're looking at this - whats the plan on bumping wordpress/php-ai-client dep to maybe "^0.4 || ^1.0 || dev-trunk"?

It would let us drop the version compare and write the calls directly. PHPStan would also gain accurate type info instead of being bypassed.

JasonTheAdams

Thanks, @Takshil-Kunadia! A couple of questions here. I'm also curious if we need the backwards-compatibility checks since thinking would fail otherwise in earlier versions. But maybe the old failure is better than an invalid method call?

JasonTheAdams · 2026-05-04T21:41:42Z

+                    if (null !== $signature) {
+                        $data['signature'] = $signature;
+                    }


Is there a condition in which the signature for a thinking part could be null? For my understanding this is a requirement and this being null would mean the data is incomplete and Anthropic is going to throw an error.

Yes Anthropic always returns signature on thinking blocks. The null check is defensive as getThoughtSignature() returns ?string, and omitting the field when null is the least-bad fallback (single-turn requests work fine without it). Happy to change to fail-fast if you prefer.

Takshil-Kunadia · 2026-05-07T10:16:15Z

Thanks, @Takshil-Kunadia! A couple of questions here. I'm also curious if we need the backwards-compatibility checks since thinking would fail otherwise in earlier versions. But maybe the old failure is better than an invalid method call?

Thinking doesn't fail on 0.4.x. It works for single-turn. The guards ensure it continues to work (degraded) rather than crashing with a fatal error or TypeError. Extended thinking works on sdk 0.4.x for single-turn requests, the code path is reachable. Its the multi-turn tool-use continuations that need signatures (added in 1.3.0). So the guards prevent crashes when a 0.4.x user hits this path rather than relying on a different failure mode upstream.

jeffpaul · 2026-08-24T17:45:41Z

@JasonTheAdams @superdav42 back to you for review

superdav42

Looks good we just need to remove the version check because we require the 1.3.1 version since this was shipped in WP 7.0

superdav42 · 2026-09-02T18:08:16Z

+                    ? $partData['signature']
+                    : null;
+                $messagePartArgs = [$partData['thinking'], MessagePartChannelEnum::thought()];
+                if (null !== $signature && version_compare(AiClient::VERSION, '1.3.0', '>=')) {


Suggested change

if (null !== $signature && version_compare(AiClient::VERSION, '1.3.0', '>=')) {

if (null !== $signature) {

superdav42 · 2026-09-02T18:09:22Z

+                if (method_exists($part, 'getThoughtSignature')) {
+                    $signature = $part->getThoughtSignature();
+                    if (null !== $signature) {
+                        $data['signature'] = $signature;
+                    }
+                }


We have php-ai-client 1.3.1 as the min required so we can remove this check now

Suggested change

if (method_exists($part, 'getThoughtSignature')) {

$signature = $part->getThoughtSignature();

if (null !== $signature) {

$data['signature'] = $signature;

}

}

$signature = $part->getThoughtSignature();

if (null !== $signature) {

$data['signature'] = $signature;

}

superdav42 · 2026-09-02T18:09:54Z


 namespace WordPress\AnthropicAiProvider\Models;

+use WordPress\AiClient\AiClient;


Suggested change

use WordPress\AiClient\AiClient;

superdav42 · 2026-09-09T17:31:56Z

Closing as superseded by #31.

JasonTheAdams requested changes May 4, 2026

View reviewed changes

Takshil-Kunadia added 3 commits May 7, 2026 15:02

feat: add thought signature support

b3f7b59

fix: add method checks

4b64c9a

refactor: remove redundant check

d39dd85

Takshil-Kunadia force-pushed the feat/thought-signature-support branch from 5b4e1df to d39dd85 Compare May 7, 2026 10:12

Takshil-Kunadia requested a review from JasonTheAdams May 7, 2026 10:16

jeffpaul added this to the 1.1.0 milestone May 13, 2026

superdav42 mentioned this pull request May 18, 2026

fix(anthropic): round-trip thinking signature for extended-thinking + tool-use Ultimate-Multisite/ai-provider-for-anthropic-max#29

Merged

3 of 4 tasks

saarnilauri mentioned this pull request Jul 21, 2026

Preserve thinking block signature in multi-turn conversations #27

Closed

jeffpaul requested a review from superdav42 August 17, 2026 18:30

raicem mentioned this pull request Aug 19, 2026

Anthropic tool continuation fails with 400 "thinking.signature: Field required" — provider plugin drops thinking signatures Automattic/haydi#14

Open

5 tasks

Merge branch 'trunk' into feat/thought-signature-support

f899c5e

jeffpaul requested a review from a team August 24, 2026 17:45

superdav42 requested changes Sep 2, 2026

View reviewed changes

superdav42 closed this Sep 9, 2026

jeffpaul removed this from the 1.0.5 milestone Oct 1, 2026

Navigation Menu

Repository navigation

feat: Thought signature support - #20

feat: Thought signature support#20
Takshil-Kunadia wants to merge 4 commits into
WordPress:trunkfrom
Takshil-Kunadia:feat/thought-signature-support

Takshil-Kunadia commented Apr 28, 2026

Uh oh!

github-actions Bot commented Apr 28, 2026 •

edited

Loading

Uh oh!

Takshil-Kunadia commented Apr 28, 2026

Uh oh!

JasonTheAdams left a comment

Uh oh!

Uh oh!

JasonTheAdams May 4, 2026

Uh oh!

Takshil-Kunadia May 7, 2026

Uh oh!

Takshil-Kunadia commented May 7, 2026

Uh oh!

jeffpaul commented Aug 24, 2026

Uh oh!

superdav42 left a comment

Uh oh!

superdav42 Sep 2, 2026

Uh oh!

superdav42 Sep 2, 2026

Uh oh!

superdav42 Sep 2, 2026

Uh oh!

superdav42 commented Sep 9, 2026

Uh oh!

Reviewers

Uh oh!

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

	if (null !== $signature && version_compare(AiClient::VERSION, '1.3.0', '>=')) {
	if (null !== $signature) {


		namespace WordPress\AnthropicAiProvider\Models;

		use WordPress\AiClient\AiClient;

Conversation

Takshil-Kunadia commented Apr 28, 2026

Summary

Test plan

Uh oh!

github-actions Bot commented Apr 28, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Takshil-Kunadia commented Apr 28, 2026

Uh oh!

JasonTheAdams left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

JasonTheAdams May 4, 2026

Choose a reason for hiding this comment

Uh oh!

Takshil-Kunadia May 7, 2026

Choose a reason for hiding this comment

Uh oh!

Takshil-Kunadia commented May 7, 2026

Uh oh!

jeffpaul commented Aug 24, 2026

Uh oh!

superdav42 left a comment

Choose a reason for hiding this comment

Uh oh!

superdav42 Sep 2, 2026

Choose a reason for hiding this comment

Uh oh!

superdav42 Sep 2, 2026

Choose a reason for hiding this comment

Uh oh!

superdav42 Sep 2, 2026

Choose a reason for hiding this comment

Uh oh!

superdav42 commented Sep 9, 2026

Uh oh!

Reviewers

Uh oh!

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

github-actions Bot commented Apr 28, 2026 •

edited

Loading