Also with Claude Sonnet 4.5, the model more effectively uses parallel tool calls, firing off multiple speculative searches simultaneously during research and reading several files at once to more quickly build context. Advanced context management in Claude Sonnet 4.5 maintains state tracking in external files, preserving goal-orientation across sessions. Combined with more-effective context window usage and new context management API features, the model optimally handles information across extended sessions to maintain coherence over time, the company said.
A new memory tool, now in beta, enables Claude Sonnet to store and retrieve information outside the context window. Also, Claude Sonnet 4.5 introduces a model_context_window_exceeded stop reason that explicitly indicates when generation stopped due to hitting the context window limit, rather than the requested max_tokens limit. This makes it easier to handle context window limits in application logic, Anthropic said. Claude Sonnet 4.5 also includes a bug fix to preserve intentional formatting in tool call string parameters.
Separately, Anthropic announced improvements in Claude Code including checkpoints, which save the user’s progress and allow them to roll back to a previous state.
