Build effective retrieval systems for deep research agents by understanding query-retriever mismatch, preferring BM25 for keyword-oriented queries, and augmenting corpus documents with metadata and LLM-generated keywords to improve information discovery.
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Build effective retrieval systems for deep research agents by understanding query-retriever mismatch, preferring BM25 for keyword-oriented queries, and augmenting corpus documents with metadata and LLM-generated keywords to improve information discovery.
SAGE: Benchmarking and Improving Retrieval for Deep Research Agents
Problem Context
Deep research agents rely heavily on retrieval systems to find relevant information, yet it's unclear which retrieval approaches effectively support complex research workflows. LLM-based retrievers often underperform because agents generate keyword-oriented sub-queries while neural retrievers expect natural language, creating a fundamental mismatch. Practitioners lack clear guidance on which retrieval strategy works for which task type.
Core Concept
SAGE introduces [corpus-level augmentation, agent-aware query understanding, BM25 preference for agents] to align retrieval systems with how agents actually generate queries. The key finding: agents decompose research problems into keyword-oriented sub-queries, making lexical retrieval (BM25) substantially outperform semantic retrievers (30% advantage on short-form questions).
Architecture Overview
Benchmark: 1,200 queries across four scientific domains; 200,000-paper corpus
Query analysis: Profile how agents decompose queries; understand agent-specific patterns
Retrieval comparison: BM25 vs. LLM-based retrievers (gte-Qwen2, ReasonIR)
Corpus augmentation: Enhance documents with metadata, keywords, summaries
Agent integration: Test retrievers within same agent framework; control for confounds
Implementation
Step 1: Build agent-aware query profiler
Analyze how research agents decompose complex queries. Profile decomposition patterns to understand retrieval behavior.
# Profile agent query decompositiondefprofile_agent_queries(agent, benchmark_queries, num_samples=100):
"""
Sample how agent decomposes research queries into sub-queries.
Analyze decomposition patterns: keyword-heavy, natural language, etc.
"""
decomposition_patterns = {
'keyword_only': 0,
'mixed': 0,
'natural_language': 0
}
for query in benchmark_queries[:num_samples]:
# Ask agent to decompose query step-by-step
sub_queries = agent.decompose_query(query)
keyword_count = (
sq sub_queries
is_keyword_only(sq)
)
ratio = keyword_count / (sub_queries)
ratio > :
decomposition_patterns[] +=
ratio > :
decomposition_patterns[] +=
:
decomposition_patterns[] +=
decomposition_patterns
# Classify decomposition
sum
1
for
in
if
len
if
0.8
'keyword_only'
1
elif
0.2
'mixed'
1
else
'natural_language'
1
return
Step 2: Implement corpus augmentation strategy
Enhance corpus documents with structured metadata and LLM-generated keywords to support multiple query modalities.
# Corpus augmentationdefaugment_corpus(documents, llm, augment_with=['keywords', 'summary']):
"""
Add metadata, keywords, and summaries to corpus documents.
Enables retrieval from diverse query patterns.
"""
augmented = []
for doc in documents:
aug_doc = {'original_text': doc['text']}
if'keywords'in augment_with:
# Extract keywords using LLM
keywords = llm.extract_keywords(
doc['text'],
max_keywords=10
)
aug_doc['keywords'] = ', '.join(keywords)
if'summary'in augment_with:
# Generate concise summary
summary = llm.summarize(
doc['text'],
max_length=100
)
aug_doc['summary'] = summary
if'metadata'in augment_with:
# Extract or infer metadata
aug_doc['metadata'] = {
'authors': extract_authors(doc),
'year': extract_year(doc),
'domains': classify_domains(doc['text'])
}
# Combine into retrievable text
augmented_text = f"""
{aug_doc['original_text']}
Keywords: {aug_doc.get('keywords', '')}
Summary: {aug_doc.get('summary', '')}
"""
aug_doc['augmented_text'] = augmented_text
augmented.append(aug_doc)
return augmented
Step 3: Compare BM25 vs. LLM-based retrievers
Systematically evaluate different retrieval approaches within the same agent framework, controlling for agent variation.
# Retriever comparisondefcompare_retrievers(agent, queries, corpus, retrievers_dict):
"""
Test multiple retrievers (BM25, neural, hybrid) with same agent.
Control for agent variation to isolate retriever impact.
"""
results = {}
for retriever_name, retriever in retrievers_dict.items():
scores = []
for query in queries:
# Retrieve top-k documents
retrieved_docs = retriever.retrieve(query, top_k=10)
# Run agent with retrieved documents
agent_output = agent.reason_with_documents(
query, retrieved_docs
)
# Evaluate agent output against reference
score = evaluate_answer_quality(
agent_output,
reference_answer=query['reference']
)
scores.append(score)
results[retriever_name] = {
'mean_score': mean(scores),
'std_dev': std(scores),
'scores': scores
}
return results
Step 4: Implement BM25 with corpus augmentation
Build BM25 retriever leveraging augmented corpus. This is the recommended baseline for agent-based retrieval.
# BM25 retriever with augmented corpusclassBM25RetrieveWithAugmentation:
def__init__(self, augmented_corpus):
from rank_bm25 import BM25Okapi
# Tokenize augmented documentsself.corpus_texts = [
doc['augmented_text'] for doc in augmented_corpus
]
self.tokenized_corpus = [
doc.lower().split() for doc inself.corpus_texts
]
# Initialize BM25self.bm25 = BM25Okapi(self.tokenized_corpus)
self.corpus_docs = augmented_corpus
defretrieve(self, query, top_k=10):
"""
Retrieve documents using BM25 on augmented corpus.
"""# Tokenize query
tokenized_query = query.lower().split()
# Score documents
scores = self.bm25.get_scores(tokenized_query)
# Get top-k
top_indices = sorted(
range(len(scores)), key=lambda i: scores[i], reverse=True
)[:top_k]
retrieved = [
{
'text': self.corpus_docs[i]['original_text'],
'augmentation': {
'keywords': self.corpus_docs[i].get('keywords'),
'summary': self.corpus_docs[i].get('summary')
},
'score': scores[i]
}
for i in top_indices
]
return retrieved
Step 5: Evaluate retrieval-agent integration
Run full evaluation loop with agent + retriever combination; measure downstream task performance.
When to use: Research agents, scientific literature discovery, multi-document reasoning tasks. Apply SAGE analysis to understand your specific agent's query patterns before choosing retriever.
Key findings:
BM25 outperforms LLM-based retrievers by ~30% on short-form questions
Agent query decomposition is keyword-oriented: optimize for this
Corpus augmentation (metadata + keywords) provides 8% lift on short-form questions
Query-retriever mismatch is the primary failure mode
Hyperparameters:
BM25 k1 (1.2-2.0): higher for more token-matching sensitivity
Top-k retrieved documents (3-10): balance coverage vs. context window
Augmentation strategy: prioritize keywords for agent-based settings; summaries for human reviewers
Common pitfalls:
Using semantic retrievers without understanding agent decomposition → misaligned queries
Over-augmentation → irrelevant noise in corpus; keep augmentation concise
Forgetting to measure retrieval quality separately; debug retrieval independently from agent reasoning
Scaling: BM25 scales efficiently to millions of documents. Augmentation adds 10-30% to index size depending on augmentation richness. Recommend periodic re-ranking of top-k with LLM rerankers for improved precision.
Reference
Paper: https://arxiv.org/abs/2602.05975
Code: Available at author's repository
Benchmark: SAGE dataset with 1,200 queries and evaluation protocols
Related work: Dense retrieval, reranking, information retrieval for agents
