give me detailed breakdown of Reddits CPA, how it has increased year over year and in last 2 quarters, how many new advertersiers added and how advertisers budget expanded and more data, I am an investor to analyze reddit stock

To evaluate Reddit’s (NYSE: RDDT) advertising monetization properly, you have to separate unit ad pricing (CPM / price per ad) from advertiser Cost Per Action (CPA).

For an equity investor, the critical dynamic in Reddit’s Q2 2026 and Q3 2026 SEC filings is an inverse divergence: Reddit’s realized price per ad (CPM) has surged over 30%+ YoY, while effective CPA for advertisers has simultaneously declined. Because conversion volumes are growing significantly faster than total ad spend, advertisers are getting cheaper unit outcomes (lower CPA) even while paying Reddit higher clearing prices per thousand impressions (higher CPM), driving massive budget expansion.

1. The Pricing & CPA Equation (YoY & Last 2 Quarters)

In its Form 10-Q filings, Reddit disaggregates advertising revenue growth into two primary levers: Ad Impressions Delivered and Average Price Per Ad. Over the past four quarters, Reddit’s growth engine flipped from being impression-led (Q4 2025) to heavily pricing-led (Q2 and Q3 2026) as auction density increased and ML ranking models improved.

Why Implied Platform CPA is Falling Despite +34% Ad Pricing:

1. The Macro Conversion Math: Blended CPA across the platform is equal to Total Performance Ad Spend÷Total Conversions\text{Total Performance Ad Spend} \div \text{Total Conversions}Total Performance Ad Spend÷Total Conversions. In Q2 2026, ad revenue grew 64% YoY while conversion volume grew over 100% YoY (2x). In Q3 2026, ad revenue grew 54% YoY while conversion volume more than tripled (>200% YoY) and click volume rose >50% YoY. Because conversion velocity (3x) is outpacing spend growth (1.54x), blended effective CPA for advertisers dropped roughly 45% to 50% YoY in Q3 2026 on a volume-adjusted basis.
2. Product-Specific CPA Reductions: Management has refrained from increasing ad load on feeds (and still runs zero ads on Reddit Search), relying instead on ML conversion modeling to lift click-through rates (CTR) and conversion rates (CVR):

• Reddit Max (AI Campaign Automation): Launched in private beta in Q1 2026 and expanded to public beta in Q3 2026. Across cohort tests, advertisers switching to Reddit Max achieved an average 17% reduction in CPA alongside a 25% lift in conversion volume.
• Dynamic Product Ads (DPA) & Shopping: DPA Return on Ad Spend (ROAS) improved 90% YoY in Q1 2026. Documented Q1–Q3 2026 case studies (such as Cozey and Ethnotek via the Shopify integration) demonstrated 28% to 40% reductions in CPA and up to 4x ROAS.
• B2B In-Market Audience Targeting: Rolled out in Q3 2026, delivering an immediate 7% average improvement (reduction) in CPA compared to standard first-party targeting.
• Engaged Video Ads: Auto-bidding tests on Reddit’s 6-second engaged-video-view objective generated a 130%+ lift in view-through rates and an 80% reduction in cost per view in Q2 2026.

2. Advertiser Additions & Channel Growth

Reddit does not disclose its exact nominal active advertiser count in quarterly filings (historically estimated above 100,000+ following its IPO), but reports exact YoY percentage expansion across its customer tiers:

• Total Active Advertisers Trajectory:

• Q4 2025: Total active advertisers grew >75% YoY.

• Q1 2026: Total active advertisers grew >75% YoY.

• Q2 2026: Total active advertisers grew >70% YoY.

• Q3 2026: Mid-market active advertisers specifically grew >50% YoY across North America and EMEA.

• The "Scaled Channel" (Mid-Market & SMBs): Reddit’s biggest customer acquisition driver is its self-serve and automated Scaled Channel, bolstered by its direct Shopify integration (launched March 2026) and Ads API ecosystem (partnerships with Smartly, Skai, Innovid, and a HubSpot beta).

• In Q2 2026, revenue from the Scaled Channel doubled (+100% YoY).

• In Q3 2026, Scaled Channel revenue grew >80% YoY, while revenue flowing through the Ads API ecosystem surged >45% quarter-over-quarter.

• Reddit Max Adoption Velocity: The number of active advertisers utilizing Reddit Max grew >60% QoQ in Q2 2026 (with Max-attributed revenue jumping >150% QoQ), and active advertiser adoption more than tripled (>200% QoQ) in Q3 2026 upon entering public beta.

3. Advertiser Budget Expansion & Wallet Share Dynamics

When an ad platform lowers an advertiser's CPA by 17%–40% while tripling conversion volume, performance marketers (who comprise over 60% of Reddit’s total ad revenue) automatically recycle those efficiency gains back into the auction to capture incremental volume until marginal ROAS normalizes.

• Agency Share-of-Wallet Expansion: According to October 2026 agency data from Horizon Media, Reddit has increased its share of overall digital advertising budgets by 20% to 25% annually over the last three years, structurally taking share from open-web DSPs like The Trade Desk (whose revenue growth slowed to single digits in 2026) as ad dollars consolidate into high-intent walled gardens.

• Vertical Breadth: In Q2 2026, 11 out of 15 tracked industry verticals grew ad spend by >50% YoY. In Q3 2026, budget expansion was led by Finance, Pharma, Retail, and Travel.

• Lower-Funnel Budget Allocation: Advertisers are aggressively shifting budgets from pure brand awareness to lower-funnel performance objectives:

• In Q2 2026, both Dynamic Product Ads (DPA) and App-Install campaign revenues more than doubled (>100% YoY), while upper-funnel video-view revenue also more than doubled YoY.

• In Q3 2026, lower-funnel shopping (supported by catalog scale expanding to 20 million products) and app-install objectives each grew >95% YoY.

• Existing Customer Spend Expansion: Management explicitly noted in Q3 2026 that the >80% YoY surge in Scaled revenue was driven not just by new logos, but by higher average spend per advertiser and deeper retention across existing cohorts.

4. Key Investor Takeaways & The Q3 2026 Traffic Overhang

While the ad stack's unit economics are firing on all cylinders, RDDT shares sold off ~25%–29% following the Q3 2026 print (October 29–30, 2026) to $91–$92/share ($18B–$19B implied market cap, ~18.7x trailing P/E). As an investor analyzing the stock, you must weigh the ad-engine strength against the top-of-funnel user headwind:

1. The Google AI Search Headwind (The Bear Thesis):

• In Q3 2026, Global DAUq grew 12% YoY to 130.3 million (flat sequentially from Q2's 130.3M), but U.S. DAUq fell 2% YoY (and 5% QoQ) to 50.7 million.
• CEO Steve Huffman warned that Google’s rollout of AI Overviews / AI Mode and demotions of machine-translated pages cut search referrals by >1 million weekly referrals on average in October 2026.
• If that referral decay persists, management warned total Q4 2026 DAUq could drop by a low-double-digit percentage from the 130M base. Consequently, Q4 2026 revenue guidance of $1.00B–$1.03B (+38% to +42% YoY) slightly missed street consensus of $1.046B.

2. Why Monetization is Insulated (The Bull Thesis):

• Logged-Out Web vs. Logged-In App: "Drive-by" Google search traffic lands on logged-out mobile web, which carries low ad load and poor targeting signal. Conversely, Logged-in DAUq and Mobile App DAUq grew sequentially in both the U.S. and Rest of World in Q3 2026, and account for over 80% of total platform ad monetization.
• Forced Login Wall Catalyst: Reddit is testing a mandatory login wall in select international markets in Q4 2026 and currently shows app-conversion prompts to only 13% of eligible mobile-web users—leaving massive headroom to convert leaking web traffic into high-ARPU app users.
• Untapped Ad Load & Search Ads: Reddit still has zero ad load on Reddit Search (over 80M+ weekly active query users) and lower feed ad load than Meta or Snap, giving it a major structural lever to expand impression supply in 2027 independent of Google traffic.

3. Capital Efficiency & Cash Generation:

• GAAP Gross Margin: 91.5% in Q3 2026 (+50 bps YoY; 9th straight quarter >90%).
• Profitability: Q3 2026 Adjusted EBITDA hit $402M (45% margin, +70% YoY); GAAP Net Income reached $283M (32% margin, +74% YoY).
• Free Cash Flow & Buybacks: Q3 FCF was $363M (41% FCF margin, +98% YoY) with CapEx at just $1M (0.1% of revenue). Reddit holds $3.03 billion in cash and marketable securities, shrank fully diluted share count by 0.3% QoQ to 206.3M shares, and has $660M remaining on its $1B buyback authorization.