diff --git a/web/src/components/StructuredReasoning.test.tsx b/web/src/components/StructuredReasoning.test.tsx
new file mode 100644
index 0000000000..d741655719
--- /dev/null
+++ b/web/src/components/StructuredReasoning.test.tsx
@@ -0,0 +1,27 @@
+import { renderToStaticMarkup } from "react-dom/server";
+import { describe, expect, it } from "vitest";
+import { StructuredReasoning } from "./StructuredReasoning";
+
+describe("StructuredReasoning", () => {
+  it("renders thinking prose without literal wrapper tags", () => {
+    const html = renderToStaticMarkup(
+      <StructuredReasoning content="<thinking>plain prose</thinking>" />,
+    );
+
+    expect(html).toContain("plain prose");
+    expect(html).not.toContain("&lt;thinking");
+    expect(html).not.toContain("&lt;/thinking");
+  });
+
+  it("renders action and result as labeled code blocks", () => {
+    const html = renderToStaticMarkup(
+      <StructuredReasoning content={'<thinking>prose <action>tool_call</action><result>{"ok":true}</result></thinking>'} />,
+    );
+
+    expect(html).toContain("prose");
+    expect(html).toContain("Action");
+    expect(html).toContain("tool_call");
+    expect(html).toContain("Result");
+    expect(html).toContain("{&quot;ok&quot;:true}");
+  });
+});
diff --git a/web/src/components/StructuredReasoning.tsx b/web/src/components/StructuredReasoning.tsx
new file mode 100644
index 0000000000..3ba6feea18
--- /dev/null
+++ b/web/src/components/StructuredReasoning.tsx
@@ -0,0 +1,58 @@
+import { useMemo } from "react";
+import { Markdown } from "@/components/Markdown";
+import {
+  parseReasoningMarkup,
+  type ReasoningMarkupSegment,
+} from "@/lib/reasoning-markup";
+
+export function StructuredReasoning({
+  content,
+  highlightTerms,
+}: {
+  content: string;
+  highlightTerms?: string[];
+}) {
+  const segments = useMemo(() => parseReasoningMarkup(content), [content]);
+
+  return (
+    <div className="space-y-2">
+      {segments.map((segment, index) => (
+        <ReasoningSegment
+          key={index}
+          segment={segment}
+          highlightTerms={highlightTerms}
+        />
+      ))}
+    </div>
+  );
+}
+
+function ReasoningSegment({
+  segment,
+  highlightTerms,
+}: {
+  segment: ReasoningMarkupSegment;
+  highlightTerms?: string[];
+}) {
+  if (segment.type === "prose") {
+    return (
+      <Markdown
+        content={segment.content.trim()}
+        highlightTerms={highlightTerms}
+      />
+    );
+  }
+
+  const label = segment.type === "action" ? "Action" : "Result";
+
+  return (
+    <div className="border border-border bg-secondary/40">
+      <div className="border-b border-border px-3 py-1 text-[11px] font-semibold uppercase tracking-wide text-text-tertiary">
+        {label}
+      </div>
+      <pre className="px-3 py-2.5 text-xs font-mono leading-relaxed overflow-x-auto whitespace-pre-wrap text-foreground">
+        <code>{segment.content}</code>
+      </pre>
+    </div>
+  );
+}
diff --git a/web/src/lib/reasoning-markup.test.ts b/web/src/lib/reasoning-markup.test.ts
new file mode 100644
index 0000000000..70083f8399
--- /dev/null
+++ b/web/src/lib/reasoning-markup.test.ts
@@ -0,0 +1,54 @@
+import { describe, expect, it } from "vitest";
+import { hasReasoningMarkup, parseReasoningMarkup } from "./reasoning-markup";
+
+describe("reasoning markup parsing", () => {
+  it("unwraps thinking prose", () => {
+    expect(parseReasoningMarkup("<thinking>plain prose</thinking>")).toEqual([
+      { type: "prose", content: "plain prose" },
+    ]);
+  });
+
+  it("separates prose from action and result segments", () => {
+    expect(
+      parseReasoningMarkup(
+        '<thinking>prose <action>tool_call</action><result>{"ok":true}</result></thinking>',
+      ),
+    ).toEqual([
+      { type: "prose", content: "prose " },
+      { type: "action", content: "tool_call" },
+      { type: "result", content: '{"ok":true}' },
+    ]);
+  });
+
+  it("does not treat unrelated angle-bracket text as reasoning markup", () => {
+    const content = "Compare <div> and <custom-tag> in prose.";
+
+    expect(hasReasoningMarkup(content)).toBe(false);
+    expect(parseReasoningMarkup(content)).toEqual([
+      { type: "prose", content },
+    ]);
+  });
+
+  it("preserves fenced XML and HTML as ordinary markdown content", () => {
+    const content = [
+      "```xml",
+      "<thinking>keep this literal</thinking>",
+      "<div>example</div>",
+      "```",
+    ].join("\n");
+
+    expect(hasReasoningMarkup(content)).toBe(false);
+    expect(parseReasoningMarkup(content)).toEqual([
+      { type: "prose", content },
+    ]);
+  });
+
+  it("leaves non-matching known tags as plain text", () => {
+    const content = "before <thinking>unfinished";
+
+    expect(hasReasoningMarkup(content)).toBe(false);
+    expect(parseReasoningMarkup(content)).toEqual([
+      { type: "prose", content },
+    ]);
+  });
+});
diff --git a/web/src/lib/reasoning-markup.ts b/web/src/lib/reasoning-markup.ts
new file mode 100644
index 0000000000..14e9c42626
--- /dev/null
+++ b/web/src/lib/reasoning-markup.ts
@@ -0,0 +1,177 @@
+export type ReasoningMarkupSegment =
+  | { type: "prose"; content: string }
+  | { type: "action"; content: string }
+  | { type: "result"; content: string };
+
+type KnownTag = "thinking" | "reflection" | "action" | "result";
+
+const KNOWN_TAGS = new Set<KnownTag>([
+  "thinking",
+  "reflection",
+  "action",
+  "result",
+]);
+const FENCE_RE = /^```/;
+const TAG_RE = /<\/?(thinking|reflection|action|result)>/gi;
+
+export function hasReasoningMarkup(content: string): boolean {
+  return splitFenceAware(content).some((chunk) => {
+    if (chunk.kind === "code") return false;
+    return findFirstCompleteKnownTag(chunk.content) !== null;
+  });
+}
+
+export function parseReasoningMarkup(content: string): ReasoningMarkupSegment[] {
+  return mergeAdjacentProse(
+    splitFenceAware(content).flatMap((chunk) =>
+      chunk.kind === "code"
+        ? [{ type: "prose" as const, content: chunk.content }]
+        : parseKnownTags(chunk.content),
+    ),
+  );
+}
+
+function parseKnownTags(content: string): ReasoningMarkupSegment[] {
+  const segments: ReasoningMarkupSegment[] = [];
+  let outputCursor = 0;
+  let searchCursor = 0;
+
+  for (;;) {
+    const opening = findNextOpeningTag(content, searchCursor);
+    if (!opening) break;
+
+    const closing = findMatchingCloseTag(content, opening.tag, opening.end);
+    if (!closing) {
+      searchCursor = opening.end;
+      continue;
+    }
+
+    if (opening.start > outputCursor) {
+      segments.push({
+        type: "prose",
+        content: content.slice(outputCursor, opening.start),
+      });
+    }
+
+    const inner = content.slice(opening.end, closing.start);
+    if (opening.tag === "action" || opening.tag === "result") {
+      segments.push({ type: opening.tag, content: inner.trim() });
+    } else {
+      segments.push(...parseKnownTags(inner));
+    }
+    outputCursor = closing.end;
+    searchCursor = closing.end;
+  }
+
+  if (outputCursor < content.length) {
+    segments.push({ type: "prose", content: content.slice(outputCursor) });
+  }
+
+  return segments.filter((segment) => segment.content.length > 0);
+}
+
+function findFirstCompleteKnownTag(content: string): KnownTag | null {
+  let cursor = 0;
+  for (;;) {
+    const opening = findNextOpeningTag(content, cursor);
+    if (!opening) return null;
+    if (findMatchingCloseTag(content, opening.tag, opening.end)) {
+      return opening.tag;
+    }
+    cursor = opening.end;
+  }
+}
+
+function findNextOpeningTag(
+  content: string,
+  from: number,
+): { tag: KnownTag; start: number; end: number } | null {
+  TAG_RE.lastIndex = from;
+  let match: RegExpExecArray | null;
+  while ((match = TAG_RE.exec(content)) !== null) {
+    const raw = match[0];
+    const tag = match[1].toLowerCase() as KnownTag;
+    if (!raw.startsWith("</") && KNOWN_TAGS.has(tag)) {
+      return { tag, start: match.index, end: TAG_RE.lastIndex };
+    }
+  }
+  return null;
+}
+
+function findMatchingCloseTag(
+  content: string,
+  tag: KnownTag,
+  from: number,
+): { start: number; end: number } | null {
+  const tagRe = new RegExp(`</?${tag}>`, "gi");
+  tagRe.lastIndex = from;
+  let depth = 1;
+  let match: RegExpExecArray | null;
+
+  while ((match = tagRe.exec(content)) !== null) {
+    if (match[0].startsWith("</")) {
+      depth -= 1;
+      if (depth === 0) {
+        return { start: match.index, end: tagRe.lastIndex };
+      }
+    } else {
+      depth += 1;
+    }
+  }
+
+  return null;
+}
+
+function splitFenceAware(
+  content: string,
+): Array<{ kind: "prose" | "code"; content: string }> {
+  const chunks: Array<{ kind: "prose" | "code"; content: string }> = [];
+  const lines = content.split("\n");
+  let buffer: string[] = [];
+  let inCode = false;
+
+  for (const line of lines) {
+    if (FENCE_RE.test(line)) {
+      if (!inCode && buffer.length > 0) {
+        chunks.push({ kind: "prose", content: buffer.join("\n") });
+        buffer = [];
+      }
+      buffer.push(line);
+
+      if (inCode) {
+        chunks.push({ kind: "code", content: buffer.join("\n") });
+        buffer = [];
+      }
+      inCode = !inCode;
+      continue;
+    }
+
+    buffer.push(line);
+  }
+
+  if (buffer.length > 0) {
+    chunks.push({
+      kind: inCode ? "code" : "prose",
+      content: buffer.join("\n"),
+    });
+  }
+
+  return chunks;
+}
+
+function mergeAdjacentProse(
+  segments: ReasoningMarkupSegment[],
+): ReasoningMarkupSegment[] {
+  const merged: ReasoningMarkupSegment[] = [];
+
+  for (const segment of segments) {
+    const prev = merged.at(-1);
+    if (prev?.type === "prose" && segment.type === "prose") {
+      prev.content += `\n${segment.content}`;
+    } else {
+      merged.push({ ...segment });
+    }
+  }
+
+  return merged;
+}
diff --git a/web/src/pages/SessionsPage.tsx b/web/src/pages/SessionsPage.tsx
index 0779086211..957e02cd9e 100644
--- a/web/src/pages/SessionsPage.tsx
+++ b/web/src/pages/SessionsPage.tsx
@@ -48,7 +48,9 @@ import type {
 } from "@/lib/api";
 import { timeAgo } from "@/lib/utils";
 import { Markdown } from "@/components/Markdown";
+import { StructuredReasoning } from "@/components/StructuredReasoning";
 import { PlatformsCard } from "@/components/PlatformsCard";
+import { hasReasoningMarkup } from "@/lib/reasoning-markup";
 import { Toast } from "@nous-research/ui/ui/components/toast";
 import { Button } from "@nous-research/ui/ui/components/button";
 import { Checkbox } from "@nous-research/ui/ui/components/checkbox";
@@ -417,6 +419,11 @@ function MessageBubble({
           <div className="text-sm text-foreground whitespace-pre-wrap leading-relaxed">
             {msg.content}
           </div>
+        ) : hasReasoningMarkup(msg.content) ? (
+          <StructuredReasoning
+            content={msg.content}
+            highlightTerms={highlightTerms}
+          />
         ) : (
           <Markdown content={msg.content} highlightTerms={highlightTerms} />
         ))}