Simplify the context truncation math

This commit is contained in:
Matt Rubens 2025-02-25 12:33:41 -05:00
parent 82b282ba01
commit d8cafbc67e
2 changed files with 122 additions and 70 deletions

View file

@ -5,6 +5,9 @@ import { Anthropic } from "@anthropic-ai/sdk"
import { ModelInfo } from "../../../shared/api"
import { truncateConversation, truncateConversationIfNeeded } from "../index"
/**
* Tests for the truncateConversation function
*/
describe("truncateConversation", () => {
it("should retain the first message", () => {
const messages: Anthropic.Messages.MessageParam[] = [
@ -91,6 +94,86 @@ describe("truncateConversation", () => {
})
})
/**
* Tests for the getMaxTokens function (private but tested through truncateConversationIfNeeded)
*/
describe("getMaxTokens", () => {
// We'll test this indirectly through truncateConversationIfNeeded
const createModelInfo = (contextWindow: number, maxTokens?: number): ModelInfo => ({
contextWindow,
supportsPromptCache: true, // Not relevant for getMaxTokens
maxTokens,
})
// Reuse across tests for consistency
const messages: Anthropic.Messages.MessageParam[] = [
{ role: "user", content: "First message" },
{ role: "assistant", content: "Second message" },
{ role: "user", content: "Third message" },
{ role: "assistant", content: "Fourth message" },
{ role: "user", content: "Fifth message" },
]
it("should use maxTokens as buffer when specified", () => {
const modelInfo = createModelInfo(100000, 50000)
// Max tokens = 100000 - 50000 = 50000
// Below max tokens - no truncation
const result1 = truncateConversationIfNeeded(messages, 49999, modelInfo)
expect(result1).toEqual(messages)
// Above max tokens - truncate
const result2 = truncateConversationIfNeeded(messages, 50001, modelInfo)
expect(result2).not.toEqual(messages)
expect(result2.length).toBe(3) // Truncated with 0.5 fraction
})
it("should use 20% of context window as buffer when maxTokens is undefined", () => {
const modelInfo = createModelInfo(100000, undefined)
// Max tokens = 100000 - (100000 * 0.2) = 80000
// Below max tokens - no truncation
const result1 = truncateConversationIfNeeded(messages, 79999, modelInfo)
expect(result1).toEqual(messages)
// Above max tokens - truncate
const result2 = truncateConversationIfNeeded(messages, 80001, modelInfo)
expect(result2).not.toEqual(messages)
expect(result2.length).toBe(3) // Truncated with 0.5 fraction
})
it("should handle small context windows appropriately", () => {
const modelInfo = createModelInfo(50000, 10000)
// Max tokens = 50000 - 10000 = 40000
// Below max tokens - no truncation
const result1 = truncateConversationIfNeeded(messages, 39999, modelInfo)
expect(result1).toEqual(messages)
// Above max tokens - truncate
const result2 = truncateConversationIfNeeded(messages, 40001, modelInfo)
expect(result2).not.toEqual(messages)
expect(result2.length).toBe(3) // Truncated with 0.5 fraction
})
it("should handle large context windows appropriately", () => {
const modelInfo = createModelInfo(200000, 30000)
// Max tokens = 200000 - 30000 = 170000
// Below max tokens - no truncation
const result1 = truncateConversationIfNeeded(messages, 169999, modelInfo)
expect(result1).toEqual(messages)
// Above max tokens - truncate
const result2 = truncateConversationIfNeeded(messages, 170001, modelInfo)
expect(result2).not.toEqual(messages)
expect(result2.length).toBe(3) // Truncated with 0.5 fraction
})
})
/**
* Tests for the truncateConversationIfNeeded function
*/
describe("truncateConversationIfNeeded", () => {
const createModelInfo = (contextWindow: number, supportsPromptCache: boolean, maxTokens?: number): ModelInfo => ({
contextWindow,
@ -106,25 +189,43 @@ describe("truncateConversationIfNeeded", () => {
{ role: "user", content: "Fifth message" },
]
it("should not truncate if tokens are below threshold for prompt caching models", () => {
const modelInfo = createModelInfo(200000, true, 50000)
const totalTokens = 100000 // Below threshold
it("should not truncate if tokens are below max tokens threshold", () => {
const modelInfo = createModelInfo(100000, true, 30000)
const maxTokens = 100000 - 30000 // 70000
const totalTokens = 69999 // Below threshold
const result = truncateConversationIfNeeded(messages, totalTokens, modelInfo)
expect(result).toEqual(messages)
expect(result).toEqual(messages) // No truncation occurs
})
it("should not truncate if tokens are below threshold for non-prompt caching models", () => {
const modelInfo = createModelInfo(200000, false)
const totalTokens = 100000 // Below threshold
it("should truncate if tokens are above max tokens threshold", () => {
const modelInfo = createModelInfo(100000, true, 30000)
const maxTokens = 100000 - 30000 // 70000
const totalTokens = 70001 // Above threshold
// When truncating, always uses 0.5 fraction
// With 4 messages after the first, 0.5 fraction means remove 2 messages
const expectedResult = [messages[0], messages[3], messages[4]]
const result = truncateConversationIfNeeded(messages, totalTokens, modelInfo)
expect(result).toEqual(messages)
expect(result).toEqual(expectedResult)
})
it("should use 80% of context window as threshold if it's greater than (contextWindow - buffer)", () => {
const modelInfo = createModelInfo(50000, true) // Small context window
const totalTokens = 40001 // Above 80% threshold (40000)
const mockResult = [messages[0], messages[3], messages[4]]
const result = truncateConversationIfNeeded(messages, totalTokens, modelInfo)
expect(result).toEqual(mockResult)
it("should work with non-prompt caching models the same as prompt caching models", () => {
// The implementation no longer differentiates between prompt caching and non-prompt caching models
const modelInfo1 = createModelInfo(100000, true, 30000)
const modelInfo2 = createModelInfo(100000, false, 30000)
// Test below threshold
const belowThreshold = 69999
expect(truncateConversationIfNeeded(messages, belowThreshold, modelInfo1)).toEqual(
truncateConversationIfNeeded(messages, belowThreshold, modelInfo2),
)
// Test above threshold
const aboveThreshold = 70001
expect(truncateConversationIfNeeded(messages, aboveThreshold, modelInfo1)).toEqual(
truncateConversationIfNeeded(messages, aboveThreshold, modelInfo2),
)
})
})

View file

@ -28,13 +28,9 @@ export function truncateConversation(
/**
* Conditionally truncates the conversation messages if the total token count exceeds the model's limit.
*
* Depending on whether the model supports prompt caching, different maximum token thresholds
* and truncation fractions are used. If the current total tokens exceed the threshold,
* the conversation is truncated using the appropriate fraction.
*
* @param {Anthropic.Messages.MessageParam[]} messages - The conversation messages.
* @param {number} totalTokens - The total number of tokens in the conversation.
* @param {ModelInfo} modelInfo - Model metadata including context window size and prompt cache support.
* @param {ModelInfo} modelInfo - Model metadata including context window size.
* @returns {Anthropic.Messages.MessageParam[]} The original or truncated conversation messages.
*/
export function truncateConversationIfNeeded(
@ -42,61 +38,16 @@ export function truncateConversationIfNeeded(
totalTokens: number,
modelInfo: ModelInfo,
): Anthropic.Messages.MessageParam[] {
if (modelInfo.supportsPromptCache) {
return totalTokens < getMaxTokensForPromptCachingModels(modelInfo)
? messages
: truncateConversation(messages, getTruncFractionForPromptCachingModels(modelInfo))
} else {
return totalTokens < getMaxTokensForNonPromptCachingModels(modelInfo)
? messages
: truncateConversation(messages, getTruncFractionForNonPromptCachingModels(modelInfo))
}
return totalTokens < getMaxTokens(modelInfo) ? messages : truncateConversation(messages, 0.5)
}
/**
* Calculates the maximum allowed tokens for models that support prompt caching.
*
* The maximum is computed as the greater of (contextWindow - buffer) and 80% of the contextWindow.
* Calculates the maximum allowed tokens
*
* @param {ModelInfo} modelInfo - The model information containing the context window size.
* @returns {number} The maximum number of tokens allowed for prompt caching models.
* @returns {number} The maximum number of tokens allowed
*/
function getMaxTokensForPromptCachingModels(modelInfo: ModelInfo): number {
// The buffer needs to be at least as large as `modelInfo.maxTokens`.
const buffer = modelInfo.maxTokens ? Math.max(40_000, modelInfo.maxTokens) : 40_000
return Math.max(modelInfo.contextWindow - buffer, modelInfo.contextWindow * 0.8)
}
/**
* Provides the fraction of messages to remove for models that support prompt caching.
*
* @param {ModelInfo} modelInfo - The model information (unused in current implementation).
* @returns {number} The truncation fraction for prompt caching models (fixed at 0.5).
*/
function getTruncFractionForPromptCachingModels(modelInfo: ModelInfo): number {
return 0.5
}
/**
* Calculates the maximum allowed tokens for models that do not support prompt caching.
*
* The maximum is computed as the greater of (contextWindow - 40000) and 80% of the contextWindow.
*
* @param {ModelInfo} modelInfo - The model information containing the context window size.
* @returns {number} The maximum number of tokens allowed for non-prompt caching models.
*/
function getMaxTokensForNonPromptCachingModels(modelInfo: ModelInfo): number {
// The buffer needs to be at least as large as `modelInfo.maxTokens`.
const buffer = modelInfo.maxTokens ? Math.max(40_000, modelInfo.maxTokens) : 40_000
return Math.max(modelInfo.contextWindow - buffer, modelInfo.contextWindow * 0.8)
}
/**
* Provides the fraction of messages to remove for models that do not support prompt caching.
*
* @param {ModelInfo} modelInfo - The model information.
* @returns {number} The truncation fraction for non-prompt caching models (fixed at 0.1).
*/
function getTruncFractionForNonPromptCachingModels(modelInfo: ModelInfo): number {
return Math.min(40_000 / modelInfo.contextWindow, 0.2)
function getMaxTokens(modelInfo: ModelInfo): number {
// The buffer needs to be at least as large as `modelInfo.maxTokens`, or 20% of the context window if for some reason it's not set.
return modelInfo.contextWindow - Math.max(modelInfo.maxTokens || modelInfo.contextWindow * 0.2)
}