Claude Code v2.1.299 Brings Idle Compaction, Enhanced Mod APIs, and Safer Eval Controls

What changed#

Anthropic released Claude Code v2.1.299, focusing on session management efficiency, mod developer tooling, and evaluation safety. The most prominent addition is automatic idle compaction. When a conversation exceeds 200,000 tokens and sits idle for roughly 54 minutes, the system compresses the history right before the one-hour prompt cache expires, preventing redundant processing on the next user message. You can adjust the minimum token threshold using CLAUDE_CODE_IDLE_COMPACT_MIN_TOKENS or disable the feature entirely by setting "idleCompaction": false in settings.json. This requires version v2.1.290 or newer.

For mod authors, the update expands available data. New environment variables like CLAUDE_CODE_DISABLE_FILE_MENTIONS let Claude receive only the file paths for @ mentions rather than loading full contents. The $.prompt.media hook now grants access to raw image and document bytes for prompts submitted through managed settings. Additionally, $.session.identity() provides authentication context, including organization and email details when forceLoginOrgUUID is configured. UI styling for mods received parallel upgrades: size, weight, mono, and tabular properties were added to Text components and spacing steps (xs through xl) within Box layouts. While bold remains functional, it is officially deprecated in favor of weight.

Operational and safety controls saw multiple additions. The claude plugin eval command now accepts --disallow-tools and a disallowed_tools configuration field, enabling testers to block built-in utilities like the Agent tool during benchmark runs. The terminal agent view gained /effort, /fast, and /model shortcuts that trigger selection menus and establish defaults for fresh sessions. A safe-mode indicator now appears in the peek panel for background processes launched with --safe-mode. Behind the scenes, --shutdown-drain-sec gives the self-hosted runner orchestrator a grace period to finish active polling and spawn hooks before terminating on SIGTERM.

Why it matters#

These changes directly address friction points in long-running development workflows and enterprise deployment pipelines. Automatic compaction reduces wasted compute cycles and keeps prompt cache hits reliable, which is critical when agents maintain extensive codebases across multiple turns. The expanded mod APIs ($.prompt.media, $.session.identity()) bridge gaps for organizations managing deployments through centralized policy files, allowing extensions to handle attachments and verify compliance contexts without workarounds.

Safety improvements around plugin evaluation and session termination prevent accidental resource exhaustion or credential exposure during testing and orchestration. If you are integrating custom gateways or managing multi-tenant setups, these controls align with the stricter hook validation and routing filters introduced in earlier patches like Claude Code Adds Deep Plugin Mods, Command Safeguards, and MCP Protocol Updates.

What to do next#

Update your local CLI to v2.1.299 to access the idle compaction logic and new environment variables. If you manage environments through a Claude Apps gateway, configure CLAUDE_CODE_ATTRIBUTION_HEADER=0 in the code policy’s env block to suppress attribution blocks, or leverage CLAUDE_CODE_DISABLE_FILE_MENTIONS to optimize memory usage during heavy @ reference usage. Mod developers should audit their CSS/styling rules to migrate away from bold toward weight, and review $.prompt.media implementations for attachment handling. Testers running plugin benchmarks should adopt --disallow-tools to isolate third-party functionality from core agent capabilities.

Limitations and caveats#

Idle compaction only triggers above the 200K-token baseline and requires approximately 54 minutes of inactivity before the cache window closes. The feature mandates v2.1.290 as a base, so older installations will not see the optimization. Managed organization settings currently skip certain mod hooks, a behavior documented in /plugin and claude plugin validate output. Additionally, while the --shutdown-drain-sec parameter improves graceful termination, it does not override hard timeouts or external process managers enforcing stricter kill signals.

Sources#

• Claude Code v2.1.299 Release Notes