Context

Module Functions

These functions are available on the Fm module directly.

Fm.context_usage_from_transcript

Fm.context_usage_from_transcript(
  transcript_json : String,
  limit : Fm::ContextLimit
) : Fm::ContextUsage

Estimates token usage from a transcript JSON string and context limit configuration.

Fm.estimate_tokens

Fm.estimate_tokens(text : String, chars_per_token : Int32) : Int32

Estimates the number of tokens in a text string using a characters-per-token heuristic.

Fm.transcript_to_text

Fm.transcript_to_text(transcript_json : String) : String

Extracts human-readable text from a transcript JSON string.

Fm.compact_transcript

Fm.compact_transcript(
  model : Fm::SystemLanguageModel,
  transcript_json : String,
  config : Fm::CompactionConfig = Fm::CompactionConfig.new
) : String

Compacts a transcript into a summary string using the on-device model.

Fm.compact_session_if_needed

Fm.compact_session_if_needed(
  model : Fm::SystemLanguageModel,
  session : Fm::Session,
  limit : Fm::ContextLimit,
  config : Fm::CompactionConfig = Fm::CompactionConfig.new,
  base_instructions : String? = nil
) : Fm::CompactedSession?

Checks if the session's context usage exceeds the limit. If so, compacts the session and returns a CompactedSession. Returns nil if compaction is not needed.

Fm.session_from_summary

Fm.session_from_summary(
  model : Fm::SystemLanguageModel,
  base_instructions : String?,
  summary : String
) : Fm::Session

Creates a new session with the summary prepended to the base instructions.

Fm::ContextLimit

Configuration for context window boundaries.

Constructor

Fm::ContextLimit.new(
  max_tokens : Int32 = 4096,
  reserved_response_tokens : Int32 = 0,
  chars_per_token : Int32 = 4
)

Class Methods

.default_on_device

Fm::ContextLimit.default_on_device : Fm::ContextLimit

Returns the default context limit for Apple's on-device models (4096 tokens).

Fm::ContextUsage

Token usage estimation results.

Fm::CompactionConfig

Controls how transcripts are summarized during compaction.

Constructor

Fm::CompactionConfig.new(
  chunk_tokens : Int32 = 800,
  max_summary_tokens : Int32 = 400,
  instructions : String = "...",
  summary_options : Fm::GenerationOptions = ...,
  chars_per_token : Int32 = 4
)

Fm::CompactedSession

Result of a successful session compaction.

Constants