Imp v0.13.0

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Imp is a framework for typed, optimizable language-model programs on the BEAM. This release changes what a tool loop's model reads. A ReActV2, ReAct or Avatar history keeps each input, tool call and tool result exactly as it was, where before anything credential-shaped in them was replaced by "[REDACTED]" on every later step. A ReActV2 step whose answer is its plain reply no longer presents that answer as a named output field. It also adds three things a host can use: a ReActV2 call can give its own tool runners, tool results record when they came back, and usage says whether a call's input token count already includes the cached prompt. A caller's model reads different requests, and a host that stores histories stores different data, so under Imp's versioning rule this is a minor release.

Install

{:imp, "~> 0.13.0"}

~> 0.13.0 takes later 0.13 patch releases and nothing newer. The two-part form, ~> 0.13, means >= 0.13.0 and < 1.0.0 in Mix, so mix deps.update imp under it takes every later 0.x release, including minor releases that change what callers receive.

Every dependency comes from Hex. Use a path dependency only while developing against a local checkout.

ExMCP and erlexec are declared runtime: false, so an OTP release that uses Imp.ACP or Imp.MCP must list applications: [ex_mcp: :load, erlexec: :load] in its release definition; see releases that use MCP or ACP. Ordinary Imp startup starts no protocol endpoint.

Changes and upgrading from 0.12

Change the Imp dependency to {:imp, "~> 0.13.0"}, run mix deps.update imp, and commit mix.lock. No data migration is needed.

  • Histories keep what the model read. Imp.Predict.ReActV2, Imp.Predict.ReAct and Imp.Predict.Avatar no longer run Imp.Redaction over each input, tool call and tool result as they add it to the history. Before, a result that only contained something credential-shaped, such as a quoted curl -H "Authorization: Bearer ..." or a JWT under discussion, was replaced whole by "[REDACTED]", and the model read that placeholder on every later step instead of what the tool returned. Run events, telemetry, traces, Imp.inspect_history/2 and saved artifacts still redact their own copies. Migration: a host that stores a history now stores what the model read. Store it privately, and use Imp.History.redact/1 or the run's events for anything shown or shipped elsewhere. A history stored before this release keeps its "[REDACTED]" strings; the original text is not recoverable from it.
  • A plain-text ReActV2 step does not present its answer as a field. In a ReActV2 step with one unconstrained text output and natively held tools, the answer is the message the model sends without a tool call. The Chat adapter's system message no longer lists that output under "Your output fields are:" or "The outputs to produce are:", and its agent and finish lines no longer name it. The finish line reads "When the final answer is ready, reply without calling a tool.", followed by the field's description if it has one. Models had been writing the field's name into the reply as a label, and the label became part of the answer. Parsing is unchanged, so a reply written in markers is still read. Signatures with submit, written tool calls, and the JSON and XML adapters are unchanged. A signature with no instructions of its own still opens with the default "Given the fields ..., produce the fields ...". Migration: a test that compares that system message exactly expects the new text.
  • Added: a ReActV2 call can give its own tool runners. Imp.call(react, %{..., tools: [tool, ...]}) uses, for that call only, the runners of the given tools in place of the program's, as a call can already give its own max_iters, last_request_note and config. Each tool must be one the program holds, with the same name, description and schema, so the request and its cacheable prefix are unchanged; anything else is refused before any request with {:error, {:invalid_react_v2_tools, message}}. The program value is not changed, and with_tools/2, the path an optimizer's updates take, still refuses a changed runner. A host can keep state that belongs to one call in that call's runners, so copies of one program called at once (by an optimizer, Imp.parallel or evaluation) never share it. See "One call's own tool runners" in the ReAct guide.
  • Added: tool results carry when they came back. ReActV2 records returned_at (ISO 8601, UTC) beside each tool result in the history, and the Chat adapter passes it to a :tool_result_renderer as %{id:, name:, returned_at:} (nil for a result recorded without one, such as one in a history saved by an earlier release). Nothing is shown by default. A host that wants the model to know the time during a tool loop renders it there. The stamp is recorded once, so every later request carries the same bytes and a cached prompt prefix survives. GEPA leaves these times out of what its reflection model reads. Two runs of the same program no longer return equal histories.
  • Added: usage says whether input includes cached tokens. A call through Imp.Clients.ReqLLM, streamed or not, carries input_includes_cached in its usage. OpenAI-style usage, as OpenAI and OpenRouter report it, counts cache reads inside the input tokens (true). Anthropic-style usage counts them apart (false). The flag is ReqLLM's own answer, the one it prices the call by, and a flag the provider's usage already carries is kept. The ATIF export's prompt_tokens for an Anthropic-style call now counts its cache reads and writes; before, it was only the tokens after the last cache breakpoint. A caller that matches a usage map exactly sees the new key.

Rollback means restoring 0.12.3 in the lock. Histories are then redacted as they are built again, the plain-text step lists its output field again, returned_at is no longer recorded (a renderer receives nil), usage loses input_includes_cached, and a call that passes tools is not given its own runners. Provider-free tests check that the next request carries a tool result as the tool returned it, for each of the three loops, along with the exact system message of a plain-text step, the time a renderer receives, a call's own runners and the refusals of tools shown differently, and the flag and ATIF prompt count for both usage shapes. This release does not establish how any particular model responds to the new system message. See the changelog for every change.

Known limits

  • The usage map (:usage on the :model_response event, Imp.Usage, Imp.Prediction.get_lm_usage/1) is ReqLLM's, with input_includes_cached added. Its :cost and :total_cost are ReqLLM's catalog estimate, not a charge, for streamed and non-streamed calls alike, and OpenRouter's charge is its "cost". Read money from cost and estimated_cost.
  • An error the provider sends inside a stream has status nil and retryable: true, because ReqLLM's stream decoder keeps only its message; the same error in a non-streamed response may carry a status that says not to retry.
  • A flat two-element name-first list that is not itself an element of a list (at the top level, in a tuple, or under a key that is not a credential name), such as ["password", "hunter2"], is not redacted, where 0.5.0 redacted it. Such a list is read as a key and value only as an element of a list, so that lists of names such as with_inputs([:api_key, :question]) survive saving.
  • The GEPA, SIMBA, MIPROv2, InferRules and random-search checkpoints redact their failure reasons but otherwise hold the resume state as it is: GEPA's candidates, evaluation cache, proposed instructions and reflection data, and the others' instructions, demos and scores. Fast-Slow and Playbook checkpoints likewise hold their prompts, rollouts and playbooks. Treat checkpoint files as sensitive.
  • A ReActV2 step whose prose quotes its own field names (a JSON object with next_thought or tool_calls keys, a [[ ## field ## ]] line, a <next_thought> tag) is not read as prose and goes to the JSON fallback, which usually costs one more call. If the model repeats the same reply, the step ends :incomplete. Beside native tool calls, such a thought becomes nil; the calls still run.
  • Tool images reach the model as user messages after the turn's tool responses, labelled with the call, not nested in the tool result, even for providers that accept images in tool results. Only MCP text and image blocks are converted; other block types stay text, image URLs in text are never fetched, and the selected model must accept image input of that format and size.
  • ATIF's extra.seen_by_model and the read-as content come from matching a tool message in the next captured request. A result that request does not carry, including one that ended the run, keeps the tool's own output and is marked unseen. agent.tool_definitions comes only from :tools_sent events, and final_metrics totals are left out when any response lacks that figure.
  • A streamed completion that the provider's content filter stops still ends as a completion: the stream's finish_reason is :content_filter and the filter's text has already arrived as chunks. Only non-streamed requests turn it into an Imp.LMError.
  • When a streamed ReqLLM request fails, ReqLLM's own warning log prints the error with its response headers. Imp strips them from the error it returns, but cannot change that log line.
  • In command output, a Bearer token of 12 to 15 characters, or one with no digit, is shown when more text or a newline follows it. 0.5.0's command pipeline hid any such token of 12 or more characters.
  • A GEPA checkpoint taken between preparing and starting a full validation resumes by rejecting that candidate, as before.

The CHANGELOG records every user-visible change in this release. Generated module documentation is the complete API reference. Start with Imp, Imp.Signature, Imp.Module, Imp.Evaluate, Imp.Optimizer, Imp.ACP, Imp.MCP, and Imp.Telemetry.