diff --git a/backend/src/cyclone/parsers/models.py b/backend/src/cyclone/parsers/models.py
index 7a2e1a4..7c66e3a 100644
--- a/backend/src/cyclone/parsers/models.py
+++ b/backend/src/cyclone/parsers/models.py
@@ -109,6 +109,8 @@ class Envelope(_Base):
     transaction_date: date
     transaction_time: str | None = None
     implementation_guide: str | None = None
+    # SP3 P1 T2: BHT06 transaction type code (was: transaction_set_purpose_code, which is BHT02).
+    transaction_type_code: str | None = None
 
 
 class BatchSummary(_Base):
@@ -135,6 +137,9 @@ class ClaimOutput(_Base):
     service_lines: list[ServiceLine] = Field(default_factory=list)
     validation: ValidationReport
     raw_segments: list[list[str]] = Field(default_factory=list)
+    # SP3 P1 T2: BHT06 transaction type code (was: transaction_set_purpose_code, which is BHT02).
+    # Mirrors envelope.transaction_type_code per parser convention.
+    transaction_type_code: str | None = None
 
 
 class ParseResult(_Base):
diff --git a/backend/src/cyclone/parsers/parse_837.py b/backend/src/cyclone/parsers/parse_837.py
index db0842e..e05c5b0 100644
--- a/backend/src/cyclone/parsers/parse_837.py
+++ b/backend/src/cyclone/parsers/parse_837.py
@@ -77,6 +77,9 @@ def _build_envelope(segments: list[list[str]], input_file: str = "") -> tuple[En
                 envelope = envelope.model_copy(update={"transaction_date": _parse_isa_date(seg[4])})
                 if len(seg) > 5:
                     envelope = envelope.model_copy(update={"transaction_time": seg[5]})
+                # SP3 P1 T2: BHT06 = transaction type code (CH/RP/etc).
+                if len(seg) > 6:
+                    envelope = envelope.model_copy(update={"transaction_type_code": seg[6]})
             except (IndexError, ValueError) as exc:
                 log.warning("Could not parse BHT date: %s", exc)
         elif seg[0] == "ST" and envelope is not None:
@@ -359,6 +362,9 @@ def parse(text: str, payer_config: PayerConfig, input_file: str = "") -> ParseRe
                         "billing_provider": provider,
                         "subscriber": subscriber,
                         "payer": payer,
+                        # SP3 P1 T2: mirror BHT06 transaction type code onto each claim
+                        # so per-claim validators (R035) can check it without re-reading the envelope.
+                        "transaction_type_code": envelope.transaction_type_code,
                     })
                     # Run validation
                     report = validate(claim, payer_config)
diff --git a/backend/src/cyclone/parsers/validator.py b/backend/src/cyclone/parsers/validator.py
index 9227798..f0cfdc8 100644
--- a/backend/src/cyclone/parsers/validator.py
+++ b/backend/src/cyclone/parsers/validator.py
@@ -57,6 +57,55 @@ def _r031_ref_g1_optional(claim: ClaimOutput, _: PayerConfig) -> Iterable[Valida
     return ()
 
 
+def _r034_ref_g1_required(claim: ClaimOutput, cfg: PayerConfig) -> Iterable[ValidationIssue]:
+    """REF*G1 is required on adjustment claims (frequency 7/8) when the payer opts in.
+
+    Gated on :attr:`PayerConfig.require_ref_g1_for_adjustments` — when the
+    payer keeps the lenient v1 default (``False``), this rule is a no-op even
+    for frequency 7/8 claims. Strict payers (e.g. CO Medicaid once it flips
+    in a future version) get the error so they can surface the missing segment
+    in their validation reports.
+    """
+    if not cfg.require_ref_g1_for_adjustments:
+        return
+    freq = claim.claim.frequency_code
+    if freq not in {"7", "8"}:
+        return
+    has_ref_g1 = any(
+        len(seg) >= 2 and seg[0] == "REF" and seg[1] == "G1"
+        for seg in claim.raw_segments
+    )
+    if not has_ref_g1:
+        yield ValidationIssue(
+            rule="R034_ref_g1_required",
+            severity="error",
+            message=(
+                f"Adjustment claim (frequency={freq}) for payer {cfg.name} requires REF*G1 "
+                "segment with prior authorization number"
+            ),
+        )
+
+
+def _r035_bht06_allowed(claim: ClaimOutput, cfg: PayerConfig) -> Iterable[ValidationIssue]:
+    """BHT06 (transaction type code, e.g. CH/RP) must be in the payer's allow-list.
+
+    Skipped silently when ``transaction_type_code`` is missing — older fixtures
+    and EDI streams without a BHT06 element should not produce a spurious error.
+    """
+    code = claim.transaction_type_code
+    if not code:
+        return
+    if code not in cfg.allowed_bht06:
+        yield ValidationIssue(
+            rule="R035_bht06_allowed",
+            severity="error",
+            message=(
+                f"BHT06 transaction type code {code!r} not in {sorted(cfg.allowed_bht06)} "
+                f"for payer {cfg.name}"
+            ),
+        )
+
+
 def _r032_clm05_2_facility_qualifier(claim: ClaimOutput, cfg: PayerConfig) -> Iterable[ValidationIssue]:
     """CLM05-2 Facility Code Qualifier must be recognized for the payer.
 
@@ -126,6 +175,8 @@ _RULES: list[Rule] = [
     _r020_npi_format,
     _r030_frequency_allowed,
     _r031_ref_g1_optional,
+    _r034_ref_g1_required,
+    _r035_bht06_allowed,
     _r032_clm05_2_facility_qualifier,
     _r033_clm05_1_place_of_service_code,
     _r050_diagnosis_present,
diff --git a/backend/tests/test_validator.py b/backend/tests/test_validator.py
index f4de62a..24d52ca 100644
--- a/backend/tests/test_validator.py
+++ b/backend/tests/test_validator.py
@@ -193,3 +193,123 @@ def test_r033_errors_with_invalid_pos_code():
     report = validate(claim, cfg)
     assert any(i.rule == "R033_clm05_1_place_of_service_code" and i.severity == "error" for i in report.errors)
     assert report.passed is False
+
+
+# --------------------------------------------------------------------------- #
+# R034 — REF*G1 enforcement (SP3 Phase 1)
+# --------------------------------------------------------------------------- #
+
+
+def _strict_cfg() -> PayerConfig:
+    """Strict cfg that mirrors the CO Medicaid defaults but turns on R034 enforcement.
+
+    We don't modify :meth:`PayerConfig.co_medicaid` — the lenient default stays
+    in v1. This local fixture lets us exercise the strict path without leaking
+    config changes across the suite.
+    """
+    return PayerConfig(
+        name="StrictTest",
+        require_ref_g1_for_adjustments=True,
+        allowed_bht06={"CH"},
+        payer_id="X",
+    )
+
+
+def test_r034_ref_g1_required_freq_7_no_ref_g1_errors():
+    cfg = _strict_cfg()
+    claim = _build_claim()
+    claim.claim.frequency_code = "7"
+    claim.raw_segments = []
+    report = validate(claim, cfg)
+    assert any(
+        i.rule == "R034_ref_g1_required" and i.severity == "error" for i in report.errors
+    )
+    assert report.passed is False
+
+
+def test_r034_ref_g1_required_freq_8_no_ref_g1_errors():
+    cfg = _strict_cfg()
+    claim = _build_claim()
+    claim.claim.frequency_code = "8"
+    claim.raw_segments = []
+    report = validate(claim, cfg)
+    assert any(
+        i.rule == "R034_ref_g1_required" and i.severity == "error" for i in report.errors
+    )
+    assert report.passed is False
+
+
+def test_r034_ref_g1_required_freq_7_with_ref_g1_passes():
+    cfg = _strict_cfg()
+    claim = _build_claim()
+    claim.claim.frequency_code = "7"
+    claim.raw_segments = [["REF", "G1", "12345"]]
+    report = validate(claim, cfg)
+    assert not any(
+        i.rule == "R034_ref_g1_required" for i in report.errors + report.warnings
+    )
+
+
+def test_r034_ref_g1_required_freq_1_no_ref_g1_passes():
+    cfg = _strict_cfg()
+    claim = _build_claim()
+    claim.claim.frequency_code = "1"
+    claim.raw_segments = []
+    report = validate(claim, cfg)
+    assert not any(
+        i.rule == "R034_ref_g1_required" for i in report.errors + report.warnings
+    )
+
+
+def test_r034_ref_g1_lenient_cfg_never_errors():
+    cfg = PayerConfig.co_medicaid()  # require_ref_g1_for_adjustments=False (lenient v1)
+    claim = _build_claim()
+    claim.claim.frequency_code = "7"
+    claim.raw_segments = []
+    report = validate(claim, cfg)
+    assert not any(
+        i.rule == "R034_ref_g1_required" for i in report.errors + report.warnings
+    )
+
+
+# --------------------------------------------------------------------------- #
+# R035 — BHT06 transaction type code (SP3 Phase 1)
+# --------------------------------------------------------------------------- #
+
+
+def test_r035_bht06_allowed_ch_passes():
+    cfg = PayerConfig.co_medicaid()
+    claim = _build_claim(transaction_type_code="CH")
+    report = validate(claim, cfg)
+    assert not any(
+        i.rule == "R035_bht06_allowed" for i in report.errors + report.warnings
+    )
+
+
+def test_r035_bht06_allowed_rp_errors_for_co_medicaid():
+    cfg = PayerConfig.co_medicaid()
+    claim = _build_claim(transaction_type_code="RP")
+    report = validate(claim, cfg)
+    assert any(
+        i.rule == "R035_bht06_allowed" and i.severity == "error" for i in report.errors
+    )
+    assert report.passed is False
+
+
+def test_r035_bht06_missing_skips():
+    cfg = PayerConfig.co_medicaid()
+    claim = _build_claim(transaction_type_code=None)
+    assert claim.transaction_type_code is None
+    report = validate(claim, cfg)
+    assert not any(
+        i.rule == "R035_bht06_allowed" for i in report.errors + report.warnings
+    )
+
+
+def test_r035_bht06_rp_allowed_for_generic_837p():
+    cfg = PayerConfig.generic_837p()  # allows {"CH", "RP"}
+    claim = _build_claim(transaction_type_code="RP")
+    report = validate(claim, cfg)
+    assert not any(
+        i.rule == "R035_bht06_allowed" for i in report.errors + report.warnings
+    )