Attest v0.4.2 Release

Released: February 22, 2026

Attest v0.4.2 is a patch release fixing three SDK bugs and adding a convenience API for both Python and TypeScript.

What Changed

LangChain Callback Protocol Fix

The LangChainCallbackHandler was missing required attributes from LangChain’s callback protocol. This caused AttributeError exceptions when LangChain introspected the handler object during chain execution. The handler now implements all required protocol attributes.

Affected users: Anyone using LangChainCallbackHandler or LangChainAdapter with LangChain 0.2+.

expect(Trace) Overload

The expect() function now accepts either an AgentResult or a raw Trace object. When a Trace is passed, it is automatically wrapped in an AgentResult.

Before (v0.4.1):

from attest import expect, AgentResult

# Had to wrap manually
result = AgentResult(trace=trace)
expect(result).output_contains("hello")

After (v0.4.2):

from attest import expect

# Pass Trace directly
expect(trace).output_contains("hello")

# AgentResult still works
expect(result).output_contains("hello")

This is useful when constructing traces manually with TraceBuilder or receiving traces from adapters that return raw Trace objects.

Plugin Async Event Loop Fix

The plugin evaluation path had an issue where submit_plugin_result could fail when called from within an already-running async event loop. The fix ensures plugin results are submitted on the engine’s dedicated background loop thread, avoiding RuntimeError: This event loop is already running errors.

Affected users: Anyone using custom plugins with the pytest-asyncio integration.

TypeScript expect(Trace) Port

The TypeScript SDK’s attestExpect() function now matches the Python SDK’s behavior — it accepts both AgentResult and raw Trace objects:

import { attestExpect, TraceBuilder } from '@attest-ai/core';

const trace = new TraceBuilder('my-agent')
  .setOutput({ message: 'hello' })
  .build();

// Pass Trace directly
attestExpect(trace).outputToContain('hello');

Version Test Improvements

Test files test_version.py and test_cli.py previously hardcoded version strings, causing test failures on every version bump. Tests now import and assert against the __version__ constant:

from attest import __version__

def test_version():
    assert __version__  # No hardcoded string

Upgrade

# Python
pip install --upgrade attest-ai

# TypeScript
npm install @attest-ai/core@0.4.2 @attest-ai/vitest@0.4.2

No breaking changes. No engine binary changes — ENGINE_VERSION remains 0.4.0.

Changelog

PR	Description
#23	LangChain callback protocol attrs, expect(Trace) overload, plugin async event loop fix
#24	Python version bump, changelog, TypeScript expect(Trace) port
#25	TypeScript version bump (package.json, version.ts)
#26	uv.lock sync
#27	Fix hardcoded version strings in test files